

<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:roleRef roleURI="http://www.merit.com/role/AccruedExpenses" xlink:href="mmsi-20161231.xsd#AccruedExpenses" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/AccruedExpensesDetails" xlink:href="mmsi-20161231.xsd#AccruedExpensesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/AccruedExpensesTables" xlink:href="mmsi-20161231.xsd#AccruedExpensesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/Acquisitions" xlink:href="mmsi-20161231.xsd#Acquisitions" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/AcquisitionsNarrativeDetails" xlink:href="mmsi-20161231.xsd#AcquisitionsNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/AcquisitionsPurchasePriceAllocationDetails" xlink:href="mmsi-20161231.xsd#AcquisitionsPurchasePriceAllocationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/AcquisitionsSummaryOfUnauditedConsolidatedResultsOfOperationsIncludingProformaResultsDetails" xlink:href="mmsi-20161231.xsd#AcquisitionsSummaryOfUnauditedConsolidatedResultsOfOperationsIncludingProformaResultsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/AcquisitionsTables" xlink:href="mmsi-20161231.xsd#AcquisitionsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/CommitmentsAndContingencies" xlink:href="mmsi-20161231.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/CommitmentsAndContingenciesNarrativeDetails" xlink:href="mmsi-20161231.xsd#CommitmentsAndContingenciesNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/CommitmentsAndContingenciesScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesDetails" xlink:href="mmsi-20161231.xsd#CommitmentsAndContingenciesScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/CommitmentsAndContingenciesTables" xlink:href="mmsi-20161231.xsd#CommitmentsAndContingenciesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/ConsolidatedBalanceSheets" xlink:href="mmsi-20161231.xsd#ConsolidatedBalanceSheets" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:href="mmsi-20161231.xsd#ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/ConsolidatedStatementsOfCashFlows" xlink:href="mmsi-20161231.xsd#ConsolidatedStatementsOfCashFlows" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/ConsolidatedStatementsOfCashFlowsParenthetical" xlink:href="mmsi-20161231.xsd#ConsolidatedStatementsOfCashFlowsParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/ConsolidatedStatementsOfComprehensiveIncome" xlink:href="mmsi-20161231.xsd#ConsolidatedStatementsOfComprehensiveIncome" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/ConsolidatedStatementsOfOperations" xlink:href="mmsi-20161231.xsd#ConsolidatedStatementsOfOperations" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/ConsolidatedStatementsOfStockholdersEquity" xlink:href="mmsi-20161231.xsd#ConsolidatedStatementsOfStockholdersEquity" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/Derivatives" xlink:href="mmsi-20161231.xsd#Derivatives" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/DerivativesAmountOfGainLossRecognizedInOciAndIncomeStatementDetails" xlink:href="mmsi-20161231.xsd#DerivativesAmountOfGainLossRecognizedInOciAndIncomeStatementDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/DerivativesFairValueOfDerivativeInstrumentsDetails" xlink:href="mmsi-20161231.xsd#DerivativesFairValueOfDerivativeInstrumentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/DerivativesForwardNotionalContractsDetails" xlink:href="mmsi-20161231.xsd#DerivativesForwardNotionalContractsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/DerivativesGainLossInConsolidatedStatementsOfIncomeDetails" xlink:href="mmsi-20161231.xsd#DerivativesGainLossInConsolidatedStatementsOfIncomeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/DerivativesNarrativeDetails" xlink:href="mmsi-20161231.xsd#DerivativesNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/DerivativesPolicies" xlink:href="mmsi-20161231.xsd#DerivativesPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/DerivativesTables" xlink:href="mmsi-20161231.xsd#DerivativesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/DocumentAndEntityInformation" xlink:href="mmsi-20161231.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/EarningsPerCommonShareEps" xlink:href="mmsi-20161231.xsd#EarningsPerCommonShareEps" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/EarningsPerCommonShareEpsDetails" xlink:href="mmsi-20161231.xsd#EarningsPerCommonShareEpsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/EarningsPerCommonShareEpsTables" xlink:href="mmsi-20161231.xsd#EarningsPerCommonShareEpsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/EmployeeBenefitPlans" xlink:href="mmsi-20161231.xsd#EmployeeBenefitPlans" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/EmployeeBenefitPlansDetails" xlink:href="mmsi-20161231.xsd#EmployeeBenefitPlansDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrants" xlink:href="mmsi-20161231.xsd#EmployeeStockPurchasePlanStockOptionsAndWarrants" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrantsAllocationOfRecognizedPeriodCostsDetails" xlink:href="mmsi-20161231.xsd#EmployeeStockPurchasePlanStockOptionsAndWarrantsAllocationOfRecognizedPeriodCostsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrantsFairValueCalculationAssumptionsDetails" xlink:href="mmsi-20161231.xsd#EmployeeStockPurchasePlanStockOptionsAndWarrantsFairValueCalculationAssumptionsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrantsNarrativeDetails" xlink:href="mmsi-20161231.xsd#EmployeeStockPurchasePlanStockOptionsAndWarrantsNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrantsOptionsOutstandingDetails" xlink:href="mmsi-20161231.xsd#EmployeeStockPurchasePlanStockOptionsAndWarrantsOptionsOutstandingDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrantsStockOptionActivityDetails" xlink:href="mmsi-20161231.xsd#EmployeeStockPurchasePlanStockOptionsAndWarrantsStockOptionActivityDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrantsTables" xlink:href="mmsi-20161231.xsd#EmployeeStockPurchasePlanStockOptionsAndWarrantsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/FairValueMeasurements" xlink:href="mmsi-20161231.xsd#FairValueMeasurements" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/FairValueMeasurementsFairValueInputsLiabilitiesQuantitativeInformationDetails" xlink:href="mmsi-20161231.xsd#FairValueMeasurementsFairValueInputsLiabilitiesQuantitativeInformationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/FairValueMeasurementsFinancialAssetsAndLiabilitiesCarriedAtFairValueDetails" xlink:href="mmsi-20161231.xsd#FairValueMeasurementsFinancialAssetsAndLiabilitiesCarriedAtFairValueDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/FairValueMeasurementsLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationDetails" xlink:href="mmsi-20161231.xsd#FairValueMeasurementsLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/FairValueMeasurementsNarrativeDetails" xlink:href="mmsi-20161231.xsd#FairValueMeasurementsNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/FairValueMeasurementsTables" xlink:href="mmsi-20161231.xsd#FairValueMeasurementsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/GoodwillAndIntangibleAssets" xlink:href="mmsi-20161231.xsd#GoodwillAndIntangibleAssets" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/GoodwillAndIntangibleAssetsFutureAmortizationExpenseDetails" xlink:href="mmsi-20161231.xsd#GoodwillAndIntangibleAssetsFutureAmortizationExpenseDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/GoodwillAndIntangibleAssetsGoodwillDetails" xlink:href="mmsi-20161231.xsd#GoodwillAndIntangibleAssetsGoodwillDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/GoodwillAndIntangibleAssetsNarrativeDetails" xlink:href="mmsi-20161231.xsd#GoodwillAndIntangibleAssetsNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/GoodwillAndIntangibleAssetsOtherIntangibleAssetsDetails" xlink:href="mmsi-20161231.xsd#GoodwillAndIntangibleAssetsOtherIntangibleAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/GoodwillAndIntangibleAssetsTables" xlink:href="mmsi-20161231.xsd#GoodwillAndIntangibleAssetsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/IncomeTaxes" xlink:href="mmsi-20161231.xsd#IncomeTaxes" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/IncomeTaxesComponentsOfIncomeTaxExpenseBenefitDetails" xlink:href="mmsi-20161231.xsd#IncomeTaxesComponentsOfIncomeTaxExpenseBenefitDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/IncomeTaxesDeferredTaxAssetsAndLiabilitiesDetails" xlink:href="mmsi-20161231.xsd#IncomeTaxesDeferredTaxAssetsAndLiabilitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/IncomeTaxesDomesticAndForeignDetails" xlink:href="mmsi-20161231.xsd#IncomeTaxesDomesticAndForeignDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/IncomeTaxesEffectiveIncomeTaxRateReconciliationDetails" xlink:href="mmsi-20161231.xsd#IncomeTaxesEffectiveIncomeTaxRateReconciliationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/IncomeTaxesNarrativeDetails" xlink:href="mmsi-20161231.xsd#IncomeTaxesNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/IncomeTaxesSummaryOfIncomeTaxContingenciesDetails" xlink:href="mmsi-20161231.xsd#IncomeTaxesSummaryOfIncomeTaxContingenciesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/IncomeTaxesTables" xlink:href="mmsi-20161231.xsd#IncomeTaxesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/Inventories" xlink:href="mmsi-20161231.xsd#Inventories" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/InventoriesDetails" xlink:href="mmsi-20161231.xsd#InventoriesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/InventoriesTables" xlink:href="mmsi-20161231.xsd#InventoriesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPolicies" xlink:href="mmsi-20161231.xsd#OrganizationAndSummaryOfSignificantAccountingPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesAccumulatedOtherComprehensiveIncomeLossDetails" xlink:href="mmsi-20161231.xsd#OrganizationAndSummaryOfSignificantAccountingPoliciesAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesConcentrationOfCreditRiskDetails" xlink:href="mmsi-20161231.xsd#OrganizationAndSummaryOfSignificantAccountingPoliciesConcentrationOfCreditRiskDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesDeferredCompensationDetails" xlink:href="mmsi-20161231.xsd#OrganizationAndSummaryOfSignificantAccountingPoliciesDeferredCompensationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesIntangibleAssetsDetails" xlink:href="mmsi-20161231.xsd#OrganizationAndSummaryOfSignificantAccountingPoliciesIntangibleAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesOrganizationDetails" xlink:href="mmsi-20161231.xsd#OrganizationAndSummaryOfSignificantAccountingPoliciesOrganizationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesOtherAssetsDetails" xlink:href="mmsi-20161231.xsd#OrganizationAndSummaryOfSignificantAccountingPoliciesOtherAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:href="mmsi-20161231.xsd#OrganizationAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesPropertyAndEquipmentDetails" xlink:href="mmsi-20161231.xsd#OrganizationAndSummaryOfSignificantAccountingPoliciesPropertyAndEquipmentDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesStockBasedCompensationDetails" xlink:href="mmsi-20161231.xsd#OrganizationAndSummaryOfSignificantAccountingPoliciesStockBasedCompensationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesTables" xlink:href="mmsi-20161231.xsd#OrganizationAndSummaryOfSignificantAccountingPoliciesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/QuarterlyResultsOfOperationsUnaudited" xlink:href="mmsi-20161231.xsd#QuarterlyResultsOfOperationsUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/QuarterlyResultsOfOperationsUnauditedDetails" xlink:href="mmsi-20161231.xsd#QuarterlyResultsOfOperationsUnauditedDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/QuarterlyResultsOfOperationsUnauditedTables" xlink:href="mmsi-20161231.xsd#QuarterlyResultsOfOperationsUnauditedTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/RevolvingCreditFacilityAndLongTermDebt" xlink:href="mmsi-20161231.xsd#RevolvingCreditFacilityAndLongTermDebt" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/RevolvingCreditFacilityAndLongTermDebtFinancialCovenantsDetails" xlink:href="mmsi-20161231.xsd#RevolvingCreditFacilityAndLongTermDebtFinancialCovenantsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/RevolvingCreditFacilityAndLongTermDebtFutureMinimumPaymentsOnLongTermDebtDetails" xlink:href="mmsi-20161231.xsd#RevolvingCreditFacilityAndLongTermDebtFutureMinimumPaymentsOnLongTermDebtDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/RevolvingCreditFacilityAndLongTermDebtNarrativeDetails" xlink:href="mmsi-20161231.xsd#RevolvingCreditFacilityAndLongTermDebtNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/RevolvingCreditFacilityAndLongTermDebtPrincipalBalancesUnderLongTermDebtDetails" xlink:href="mmsi-20161231.xsd#RevolvingCreditFacilityAndLongTermDebtPrincipalBalancesUnderLongTermDebtDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/RevolvingCreditFacilityAndLongTermDebtTables" xlink:href="mmsi-20161231.xsd#RevolvingCreditFacilityAndLongTermDebtTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/RoyaltyAgreements" xlink:href="mmsi-20161231.xsd#RoyaltyAgreements" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/RoyaltyAgreementsNarrativeDetails" xlink:href="mmsi-20161231.xsd#RoyaltyAgreementsNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/ScheduleIiValuationAndQualifyingAccounts" xlink:href="mmsi-20161231.xsd#ScheduleIiValuationAndQualifyingAccounts" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/ScheduleIiValuationAndQualifyingAccountsDetails" xlink:href="mmsi-20161231.xsd#ScheduleIiValuationAndQualifyingAccountsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/SegmentReportingAndForeignOperations" xlink:href="mmsi-20161231.xsd#SegmentReportingAndForeignOperations" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/SegmentReportingAndForeignOperationsAssetsDetails" xlink:href="mmsi-20161231.xsd#SegmentReportingAndForeignOperationsAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/SegmentReportingAndForeignOperationsLongLivedAssetsByGeographicAreaDetails" xlink:href="mmsi-20161231.xsd#SegmentReportingAndForeignOperationsLongLivedAssetsByGeographicAreaDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/SegmentReportingAndForeignOperationsNarrativeDetails" xlink:href="mmsi-20161231.xsd#SegmentReportingAndForeignOperationsNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/SegmentReportingAndForeignOperationsOperatingIncomeDetails" xlink:href="mmsi-20161231.xsd#SegmentReportingAndForeignOperationsOperatingIncomeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/SegmentReportingAndForeignOperationsSalesByBusinessSegmentDetails" xlink:href="mmsi-20161231.xsd#SegmentReportingAndForeignOperationsSalesByBusinessSegmentDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/SegmentReportingAndForeignOperationsTables" xlink:href="mmsi-20161231.xsd#SegmentReportingAndForeignOperationsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/SubsequentEvents" xlink:href="mmsi-20161231.xsd#SubsequentEvents" xlink:type="simple" />
  <link:roleRef roleURI="http://www.merit.com/role/SubsequentEventsDetails" xlink:href="mmsi-20161231.xsd#SubsequentEventsDetails" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <link:definitionLink xlink:role="http://www.merit.com/role/AccruedExpenses" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/AccruedExpensesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/AccruedExpensesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/Acquisitions" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/AcquisitionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_9F2CC350B3BA4A6FF1E98173C911327E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_9F2CC350B3BA4A6FF1E98173C911327E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_C4E82F77FA97E83160128173C911F6FE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_9F2CC350B3BA4A6FF1E98173C911327E" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_C4E82F77FA97E83160128173C911F6FE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_F4F10196A724D2B468DA8173C9115944_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_C4E82F77FA97E83160128173C911F6FE" xlink:to="loc_us-gaap_RelatedPartyDomain_F4F10196A724D2B468DA8173C9115944_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_F4F10196A724D2B468DA8173C9115944" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_C4E82F77FA97E83160128173C911F6FE" xlink:to="loc_us-gaap_RelatedPartyDomain_F4F10196A724D2B468DA8173C9115944" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_InvesteeMember" xlink:label="loc_us-gaap_InvesteeMember_51F27884D31547601EA28173C911C566" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_F4F10196A724D2B468DA8173C9115944" xlink:to="loc_us-gaap_InvesteeMember_51F27884D31547601EA28173C911C566" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LimitedLiabilityCompanyMember" xlink:label="loc_us-gaap_LimitedLiabilityCompanyMember_3A26612AEB46BA076C748173C911460C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_F4F10196A724D2B468DA8173C9115944" xlink:to="loc_us-gaap_LimitedLiabilityCompanyMember_3A26612AEB46BA076C748173C911460C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_4C4130C1F74159B4CF148173C9126C93" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_9F2CC350B3BA4A6FF1E98173C911327E" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_4C4130C1F74159B4CF148173C9126C93" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_5C6312A543A5C8B954AE8173C9126774_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_4C4130C1F74159B4CF148173C9126C93" xlink:to="loc_us-gaap_SegmentDomain_5C6312A543A5C8B954AE8173C9126774_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_5C6312A543A5C8B954AE8173C9126774" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_4C4130C1F74159B4CF148173C9126C93" xlink:to="loc_us-gaap_SegmentDomain_5C6312A543A5C8B954AE8173C9126774" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CardiovascularSegmentMember" xlink:label="loc_mmsi_CardiovascularSegmentMember_11E6AFE6D7C97E7AC0898173C9124FD9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_5C6312A543A5C8B954AE8173C9126774" xlink:to="loc_mmsi_CardiovascularSegmentMember_11E6AFE6D7C97E7AC0898173C9124FD9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:label="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_EFBC596BAB1BBF0E53498173C912A06B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_9F2CC350B3BA4A6FF1E98173C911327E" xlink:to="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_EFBC596BAB1BBF0E53498173C912A06B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ReceivableTypeDomain" xlink:label="loc_us-gaap_ReceivableTypeDomain_6A93891A1EA4525ACAF88173C912C8FC_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_EFBC596BAB1BBF0E53498173C912A06B" xlink:to="loc_us-gaap_ReceivableTypeDomain_6A93891A1EA4525ACAF88173C912C8FC_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ReceivableTypeDomain" xlink:label="loc_us-gaap_ReceivableTypeDomain_6A93891A1EA4525ACAF88173C912C8FC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_EFBC596BAB1BBF0E53498173C912A06B" xlink:to="loc_us-gaap_ReceivableTypeDomain_6A93891A1EA4525ACAF88173C912C8FC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LoansReceivableMember" xlink:label="loc_us-gaap_LoansReceivableMember_6C67A05332FE3C8749668173C9123C9B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_6A93891A1EA4525ACAF88173C912C8FC" xlink:to="loc_us-gaap_LoansReceivableMember_6C67A05332FE3C8749668173C9123C9B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GainLossOnInvestmentsByCategoryAxis" xlink:label="loc_us-gaap_GainLossOnInvestmentsByCategoryAxis_C696876B86C5B4056D5A8173C91336BF" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_9F2CC350B3BA4A6FF1E98173C911327E" xlink:to="loc_us-gaap_GainLossOnInvestmentsByCategoryAxis_C696876B86C5B4056D5A8173C91336BF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:label="loc_us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain_F859D9C5CAB7D1F3CC448173C9137376_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GainLossOnInvestmentsByCategoryAxis_C696876B86C5B4056D5A8173C91336BF" xlink:to="loc_us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain_F859D9C5CAB7D1F3CC448173C9137376_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:label="loc_us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain_F859D9C5CAB7D1F3CC448173C9137376" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GainLossOnInvestmentsByCategoryAxis_C696876B86C5B4056D5A8173C91336BF" xlink:to="loc_us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain_F859D9C5CAB7D1F3CC448173C9137376" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CostmethodInvestmentsMember" xlink:label="loc_us-gaap_CostmethodInvestmentsMember_017DF36F1477009BA2068173C913D55B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain_F859D9C5CAB7D1F3CC448173C9137376" xlink:to="loc_us-gaap_CostmethodInvestmentsMember_017DF36F1477009BA2068173C913D55B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CounterpartyNameAxis" xlink:label="loc_us-gaap_CounterpartyNameAxis_40C5A0E639F7A0D01F938173C9130FEC" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_9F2CC350B3BA4A6FF1E98173C911327E" xlink:to="loc_us-gaap_CounterpartyNameAxis_40C5A0E639F7A0D01F938173C9130FEC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CounterpartyNameAxis_40C5A0E639F7A0D01F938173C9130FEC" xlink:to="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CounterpartyNameAxis_40C5A0E639F7A0D01F938173C9130FEC" xlink:to="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BluegrassVascularTechnologiesInc.Member" xlink:label="loc_mmsi_BluegrassVascularTechnologiesInc.Member_0A95D419304DC8D7B6628173C9134AAF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:to="loc_mmsi_BluegrassVascularTechnologiesInc.Member_0A95D419304DC8D7B6628173C9134AAF" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CagentVascularLLCMember" xlink:label="loc_mmsi_CagentVascularLLCMember_02EDE4824A43FAB168578173C913521A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:to="loc_mmsi_CagentVascularLLCMember_02EDE4824A43FAB168578173C913521A" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_MedicalCompany1Member" xlink:label="loc_mmsi_MedicalCompany1Member_21C44BAC1BE53E59F36F8173C914DEE5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:to="loc_mmsi_MedicalCompany1Member_21C44BAC1BE53E59F36F8173C914DEE5" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BlockadeMedicalLlcMember" xlink:label="loc_mmsi_BlockadeMedicalLlcMember_930DC1B5D8FA854A12AD8173C914C1B6" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:to="loc_mmsi_BlockadeMedicalLlcMember_930DC1B5D8FA854A12AD8173C914C1B6" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_LeMaitreVascularInc.Member" xlink:label="loc_mmsi_LeMaitreVascularInc.Member_FA5A7ABAA3973074D8B78173C914D03F" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:to="loc_mmsi_LeMaitreVascularInc.Member_FA5A7ABAA3973074D8B78173C914D03F" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CatchMedicalLLCMember" xlink:label="loc_mmsi_CatchMedicalLLCMember_0413433CBF451E7F09568173C914ED94" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:to="loc_mmsi_CatchMedicalLLCMember_0413433CBF451E7F09568173C914ED94" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_DistalAccessLLCMember" xlink:label="loc_mmsi_DistalAccessLLCMember_BC065BDDBE1D25D5B7998173C914CFF3" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:to="loc_mmsi_DistalAccessLLCMember_BC065BDDBE1D25D5B7998173C914CFF3" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_TeleflexIncorporatedMember" xlink:label="loc_mmsi_TeleflexIncorporatedMember_D07392EF03A734A9359F8173C9147854" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:to="loc_mmsi_TeleflexIncorporatedMember_D07392EF03A734A9359F8173C9147854" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CatheterConnectionsInc.Member" xlink:label="loc_mmsi_CatheterConnectionsInc.Member_FCF180A7972DBBABEE2A8173C9148B2D" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:to="loc_mmsi_CatheterConnectionsInc.Member_FCF180A7972DBBABEE2A8173C9148B2D" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_MedicalCompany2Member" xlink:label="loc_mmsi_MedicalCompany2Member_9CD6E2FE0CB06932DD538173C9143B4E" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:to="loc_mmsi_MedicalCompany2Member_9CD6E2FE0CB06932DD538173C9143B4E" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_MedicalCompany3Member" xlink:label="loc_mmsi_MedicalCompany3Member_2EA322A2BF056889C8068173C914D2F1" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C7C02C6F1B213DD0EE0B8173C9132E1D" xlink:to="loc_mmsi_MedicalCompany3Member_2EA322A2BF056889C8068173C914D2F1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_194B80DAEF2325B5E8A98173C915078E" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_9F2CC350B3BA4A6FF1E98173C911327E" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_194B80DAEF2325B5E8A98173C915078E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LossContingencyNatureDomain" xlink:label="loc_us-gaap_LossContingencyNatureDomain_BD3BF00C840EE62B82F38173C9153AAF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_194B80DAEF2325B5E8A98173C915078E" xlink:to="loc_us-gaap_LossContingencyNatureDomain_BD3BF00C840EE62B82F38173C9153AAF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LossContingencyNatureDomain" xlink:label="loc_us-gaap_LossContingencyNatureDomain_BD3BF00C840EE62B82F38173C9153AAF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_194B80DAEF2325B5E8A98173C915078E" xlink:to="loc_us-gaap_LossContingencyNatureDomain_BD3BF00C840EE62B82F38173C9153AAF" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_AdditionalPaymentsforLicenseAgreementMilestoneMember" xlink:label="loc_mmsi_AdditionalPaymentsforLicenseAgreementMilestoneMember_B9FB1176F26460F06F8F8173C9155669" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_BD3BF00C840EE62B82F38173C9153AAF" xlink:to="loc_mmsi_AdditionalPaymentsforLicenseAgreementMilestoneMember_B9FB1176F26460F06F8F8173C9155669" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_0D8155B25529235F42FB8173C915A546" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_9F2CC350B3BA4A6FF1E98173C911327E" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_0D8155B25529235F42FB8173C915A546" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6BA0579096043EF0A7378173C91512DB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_0D8155B25529235F42FB8173C915A546" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6BA0579096043EF0A7378173C91512DB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6BA0579096043EF0A7378173C91512DB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_0D8155B25529235F42FB8173C915A546" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6BA0579096043EF0A7378173C91512DB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LicensingAgreementsMember" xlink:label="loc_us-gaap_LicensingAgreementsMember_2CAD1330AD8250BF1A298173C915D192" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6BA0579096043EF0A7378173C91512DB" xlink:to="loc_us-gaap_LicensingAgreementsMember_2CAD1330AD8250BF1A298173C915D192" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_74D94102D1E7CB5FA1588173C915A477" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6BA0579096043EF0A7378173C91512DB" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_74D94102D1E7CB5FA1588173C915A477" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CustomerListsMember" xlink:label="loc_us-gaap_CustomerListsMember_F15869A891005D6407D38173C91529FD" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6BA0579096043EF0A7378173C91512DB" xlink:to="loc_us-gaap_CustomerListsMember_F15869A891005D6407D38173C91529FD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DistributionRightsMember" xlink:label="loc_us-gaap_DistributionRightsMember_E6B8C8E3FEDFF696DDDC8173C9161EAA" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6BA0579096043EF0A7378173C91512DB" xlink:to="loc_us-gaap_DistributionRightsMember_E6B8C8E3FEDFF696DDDC8173C9161EAA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TrademarksMember" xlink:label="loc_us-gaap_TrademarksMember_52621B77E6B5F948F0F18173C916ACCA" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6BA0579096043EF0A7378173C91512DB" xlink:to="loc_us-gaap_TrademarksMember_52621B77E6B5F948F0F18173C916ACCA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_F6B58E3C40E4B13766218173C9163E22" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_9F2CC350B3BA4A6FF1E98173C911327E" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_F6B58E3C40E4B13766218173C9163E22" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2025FB9D9FBDE092A41E8173C91699AF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_F6B58E3C40E4B13766218173C9163E22" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2025FB9D9FBDE092A41E8173C91699AF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2025FB9D9FBDE092A41E8173C91699AF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_F6B58E3C40E4B13766218173C9163E22" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2025FB9D9FBDE092A41E8173C91699AF" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BluegrassVascularTechnologiesInc.Member" xlink:label="loc_mmsi_BluegrassVascularTechnologiesInc.Member_F2A1F2D87897134816388173C9161399" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2025FB9D9FBDE092A41E8173C91699AF" xlink:to="loc_mmsi_BluegrassVascularTechnologiesInc.Member_F2A1F2D87897134816388173C9161399" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_DFINEInc.Member" xlink:label="loc_mmsi_DFINEInc.Member_6C50A6B26D81F8B631878173C916467A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2025FB9D9FBDE092A41E8173C91699AF" xlink:to="loc_mmsi_DFINEInc.Member_6C50A6B26D81F8B631878173C916467A" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_HeROGraftMember" xlink:label="loc_mmsi_HeROGraftMember_741CF1FAD1F140D533008173C9163B5D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2025FB9D9FBDE092A41E8173C91699AF" xlink:to="loc_mmsi_HeROGraftMember_741CF1FAD1F140D533008173C9163B5D" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CardiovascularSegmentMember" xlink:label="loc_mmsi_CardiovascularSegmentMember_02C4B025A850C4EF06068173C916FDD2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2025FB9D9FBDE092A41E8173C91699AF" xlink:to="loc_mmsi_CardiovascularSegmentMember_02C4B025A850C4EF06068173C916FDD2" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_XablecathInc.Member" xlink:label="loc_mmsi_XablecathInc.Member_D5D1D42C7374C689E18B8173C9172B60" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2025FB9D9FBDE092A41E8173C91699AF" xlink:to="loc_mmsi_XablecathInc.Member_D5D1D42C7374C689E18B8173C9172B60" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_QuellentLLCMember" xlink:label="loc_mmsi_QuellentLLCMember_5C19E2DB836B547D5E9F8173C917C664" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2025FB9D9FBDE092A41E8173C91699AF" xlink:to="loc_mmsi_QuellentLLCMember_5C19E2DB836B547D5E9F8173C917C664" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_LimitedLiabilityCompanyAcquisitionMember" xlink:label="loc_mmsi_LimitedLiabilityCompanyAcquisitionMember_01D82E5CE3993E248F328173C917A273" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2025FB9D9FBDE092A41E8173C91699AF" xlink:to="loc_mmsi_LimitedLiabilityCompanyAcquisitionMember_01D82E5CE3993E248F328173C917A273" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_GMedixMember" xlink:label="loc_mmsi_GMedixMember_0FEA52548490805E031A8173C917A247" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2025FB9D9FBDE092A41E8173C91699AF" xlink:to="loc_mmsi_GMedixMember_0FEA52548490805E031A8173C917A247" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PaymentsToAcquireInvestments" xlink:label="loc_us-gaap_PaymentsToAcquireInvestments_EAD189A356A8DAB4F4298173C9187B6C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_PaymentsToAcquireInvestments_EAD189A356A8DAB4F4298173C9187B6C" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CostMethodInvestmentsInterestAcquiredNumberOfUnits" xlink:label="loc_mmsi_CostMethodInvestmentsInterestAcquiredNumberOfUnits_3D2005FD4ED998B9F94F8173C918F66A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_mmsi_CostMethodInvestmentsInterestAcquiredNumberOfUnits_3D2005FD4ED998B9F94F8173C918F66A" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CostMethodInvestmentsOwnershipPercentage" xlink:label="loc_mmsi_CostMethodInvestmentsOwnershipPercentage_4D9FA7BF00C8B6AFE8A98173C9183E48" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_mmsi_CostMethodInvestmentsOwnershipPercentage_4D9FA7BF00C8B6AFE8A98173C9183E48" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CostMethodInvestments" xlink:label="loc_us-gaap_CostMethodInvestments_5ED4242B35A1664554E28173C918ABF9" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_CostMethodInvestments_5ED4242B35A1664554E28173C918ABF9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_CC327F59E424A75D00B88173C9181F71" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_CC327F59E424A75D00B88173C9181F71" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_5134B0E9E61293D912548173C9186283" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_5134B0E9E61293D912548173C9186283" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_7A1077C74D5C96946BC88173C91813AE" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_7A1077C74D5C96946BC88173C91813AE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredOther1" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredOther1_E7A28EBC22E1FB629C4B8173C919364B" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredOther1_E7A28EBC22E1FB629C4B8173C919364B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred_C7BF04266AAC88D3F6128173C9191E23" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred_C7BF04266AAC88D3F6128173C9191E23" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory_A6011A2689A2E55BD8998173C9195AF9" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory_A6011A2689A2E55BD8998173C9195AF9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPropertyPlantAndEquipment" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPropertyPlantAndEquipment_AA4823E6EF0A6334B5E68173C919032F" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPropertyPlantAndEquipment_AA4823E6EF0A6334B5E68173C919032F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_8EC0AB6B8DBBE3CC36848173C919D4FC" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_8EC0AB6B8DBBE3CC36848173C919D4FC" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedExpenses" xlink:label="loc_mmsi_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedExpenses_F84770780E9CFED1B5E78173C9194FA4" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_mmsi_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedExpenses_F84770780E9CFED1B5E78173C9194FA4" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiabilities" xlink:label="loc_mmsi_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiabilities_AE4ED0DD3A3E002231428173C919E6C6" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_mmsi_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiabilities_AE4ED0DD3A3E002231428173C919E6C6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_F4F67E2F067931A485EC8173C91ACEAE" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_F4F67E2F067931A485EC8173C91ACEAE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_92EE93F3B72B448E92658173C91A506E" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_92EE93F3B72B448E92658173C91A506E" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentAssetsTradeReceivablesGross" xlink:label="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentAssetsTradeReceivablesGross_19CFF0AFDA1A8EA86E558173C91A1014" xlink:type="locator" />
    <link:definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentAssetsTradeReceivablesGross_19CFF0AFDA1A8EA86E558173C91A1014" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentAssetsTradeReceivablesAllowanceforDoubtfulAccounts" xlink:label="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentAssetsTradeReceivablesAllowanceforDoubtfulAccounts_F7E343EDB59A1A2C8FFC8173C91AA6C8" xlink:type="locator" />
    <link:definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentAssetsTradeReceivablesAllowanceforDoubtfulAccounts_F7E343EDB59A1A2C8FFC8173C91AA6C8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_E24F557AB5218F54F9E48173C91AA297" xlink:type="locator" />
    <link:definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_E24F557AB5218F54F9E48173C91AA297" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_A9640B5FA213EAC8B6FC8173C91A607A" xlink:type="locator" />
    <link:definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_A9640B5FA213EAC8B6FC8173C91A607A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PaymentsToAcquireIntangibleAssets" xlink:label="loc_us-gaap_PaymentsToAcquireIntangibleAssets_84711EE1E8AB8762E1918173C91A3533" xlink:type="locator" />
    <link:definitionArc order="21" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_PaymentsToAcquireIntangibleAssets_84711EE1E8AB8762E1918173C91A3533" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedLicenseAgreementsGross" xlink:label="loc_us-gaap_FiniteLivedLicenseAgreementsGross_6B8F44BB811C9444E0EC8173C91A3948" xlink:type="locator" />
    <link:definitionArc order="22" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_FiniteLivedLicenseAgreementsGross_6B8F44BB811C9444E0EC8173C91A3948" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_AcquisitionPurchasesinAccruedExpenses" xlink:label="loc_mmsi_AcquisitionPurchasesinAccruedExpenses_2641F92C9EFE00C0BF698173C91A5189" xlink:type="locator" />
    <link:definitionArc order="23" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_mmsi_AcquisitionPurchasesinAccruedExpenses_2641F92C9EFE00C0BF698173C91A5189" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_D6AD1B2A934B356702758173C91B926A" xlink:type="locator" />
    <link:definitionArc order="24" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_D6AD1B2A934B356702758173C91B926A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillAcquiredDuringPeriod" xlink:label="loc_us-gaap_GoodwillAcquiredDuringPeriod_15821590A0BD7FB8333A8173C91B6968" xlink:type="locator" />
    <link:definitionArc order="25" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_GoodwillAcquiredDuringPeriod_15821590A0BD7FB8333A8173C91B6968" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOff" xlink:label="loc_us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOff_131B8FE99AF2EE24A2968173C91B7721" xlink:type="locator" />
    <link:definitionArc order="26" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOff_131B8FE99AF2EE24A2968173C91B7721" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_AcquisitionPurchasesinLongtermObligations" xlink:label="loc_mmsi_AcquisitionPurchasesinLongtermObligations_58AD0BBBDE108692DD8C8173C91B8547" xlink:type="locator" />
    <link:definitionArc order="27" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_mmsi_AcquisitionPurchasesinLongtermObligations_58AD0BBBDE108692DD8C8173C91B8547" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_FuturePaymentsUnderPurchaseAgreement" xlink:label="loc_mmsi_FuturePaymentsUnderPurchaseAgreement_E85DA5609AAEC3510A738173C91B31BA" xlink:type="locator" />
    <link:definitionArc order="28" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_mmsi_FuturePaymentsUnderPurchaseAgreement_E85DA5609AAEC3510A738173C91B31BA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_844DA358D4968938541F8173C91BB825" xlink:type="locator" />
    <link:definitionArc order="29" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_844DA358D4968938541F8173C91BB825" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_FinitelivedIntangibleAssetsAcquiredLiabilitiesIncurred" xlink:label="loc_mmsi_FinitelivedIntangibleAssetsAcquiredLiabilitiesIncurred_A76B49F9AE3A059AC0748173C91BFB14" xlink:type="locator" />
    <link:definitionArc order="30" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_mmsi_FinitelivedIntangibleAssetsAcquiredLiabilitiesIncurred_A76B49F9AE3A059AC0748173C91BFB14" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_5693D39F2795DC5724A98173C91BA08B" xlink:type="locator" />
    <link:definitionArc order="31" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_5693D39F2795DC5724A98173C91BA08B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_BC11212A7ED2A02EEA6D8173C91B37E3" xlink:type="locator" />
    <link:definitionArc order="32" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_57413EC29EFF9138F8618173C917818D" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_BC11212A7ED2A02EEA6D8173C91B37E3" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/AcquisitionsPurchasePriceAllocationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_8E8F26D2FC845AFACCE1811DF0FF99C5" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_E2CFB15ABAA39610C4A6811DF0F85F26" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8E8F26D2FC845AFACCE1811DF0FF99C5" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_E2CFB15ABAA39610C4A6811DF0F85F26" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_40C9F35CF6518DF9A28F811DF0F8EF2D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_E2CFB15ABAA39610C4A6811DF0F85F26" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_40C9F35CF6518DF9A28F811DF0F8EF2D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_BD53BF60020E905C1579811DF0FC8A73_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_40C9F35CF6518DF9A28F811DF0F8EF2D" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_BD53BF60020E905C1579811DF0FC8A73_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_BD53BF60020E905C1579811DF0FC8A73" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_40C9F35CF6518DF9A28F811DF0F8EF2D" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_BD53BF60020E905C1579811DF0FC8A73" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_39DF6D5F301BEA68F282811DF0FD4E3C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_BD53BF60020E905C1579811DF0FC8A73" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_39DF6D5F301BEA68F282811DF0FD4E3C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CustomerListsMember" xlink:label="loc_us-gaap_CustomerListsMember_96E26C985965F5714D8A811DF0FD1706" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_BD53BF60020E905C1579811DF0FC8A73" xlink:to="loc_us-gaap_CustomerListsMember_96E26C985965F5714D8A811DF0FD1706" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TrademarksMember" xlink:label="loc_us-gaap_TrademarksMember_622022704B50D010882F811DF0FD116E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_BD53BF60020E905C1579811DF0FC8A73" xlink:to="loc_us-gaap_TrademarksMember_622022704B50D010882F811DF0FD116E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_E98F66027716BF1124E6811DF0FD4106" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_E2CFB15ABAA39610C4A6811DF0F85F26" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_E98F66027716BF1124E6811DF0FD4106" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2BE6F934F293197BA58E811DF0FED055_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_E98F66027716BF1124E6811DF0FD4106" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2BE6F934F293197BA58E811DF0FED055_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2BE6F934F293197BA58E811DF0FED055" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_E98F66027716BF1124E6811DF0FD4106" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2BE6F934F293197BA58E811DF0FED055" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_HeROGraftMember" xlink:label="loc_mmsi_HeROGraftMember_6295F5981CC0CA097D02811DF0FEEC18" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2BE6F934F293197BA58E811DF0FED055" xlink:to="loc_mmsi_HeROGraftMember_6295F5981CC0CA097D02811DF0FEEC18" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_DFINEInc.Member" xlink:label="loc_mmsi_DFINEInc.Member_75AED09EB33ECD6111F2811DF0FFA979" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2BE6F934F293197BA58E811DF0FED055" xlink:to="loc_mmsi_DFINEInc.Member_75AED09EB33ECD6111F2811DF0FFA979" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_A53DBA8B397F1824E2B6811DF0FF8B3C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8E8F26D2FC845AFACCE1811DF0FF99C5" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_A53DBA8B397F1824E2B6811DF0FF8B3C" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentAssetsTradeReceivables" xlink:label="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentAssetsTradeReceivables_68E0916CF82D1C992C7C811DF0FF3711" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_A53DBA8B397F1824E2B6811DF0FF8B3C" xlink:to="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentAssetsTradeReceivables_68E0916CF82D1C992C7C811DF0FF3711" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentAssetsOtherReceivables" xlink:label="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentAssetsOtherReceivables_67A9FBE912D1B6884EC6811DF0FF1E8A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_A53DBA8B397F1824E2B6811DF0FF8B3C" xlink:to="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentAssetsOtherReceivables_67A9FBE912D1B6884EC6811DF0FF1E8A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_2AD7563593470F82280B811DF1006AD5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_A53DBA8B397F1824E2B6811DF0FF8B3C" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_2AD7563593470F82280B811DF1006AD5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_5DC89A5E0EBB113BC14B811DF1006BA3" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_A53DBA8B397F1824E2B6811DF0FF8B3C" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_5DC89A5E0EBB113BC14B811DF1006BA3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_42D9176A47ADAA175F40811DF1014711" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_A53DBA8B397F1824E2B6811DF0FF8B3C" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_42D9176A47ADAA175F40811DF1014711" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_17BB89A6F7D3C56F1E0F811DF1014F3E" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_A53DBA8B397F1824E2B6811DF0FF8B3C" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_17BB89A6F7D3C56F1E0F811DF1014F3E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_948EB97ED3B5266F37C5811DF101E346" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_A53DBA8B397F1824E2B6811DF0FF8B3C" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_948EB97ED3B5266F37C5811DF101E346" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_FE872AFA1B9E009A4784811DF101E635" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_A53DBA8B397F1824E2B6811DF0FF8B3C" xlink:to="loc_us-gaap_Goodwill_FE872AFA1B9E009A4784811DF101E635" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsIncludingGoodwill" xlink:label="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsIncludingGoodwill_EFF321BD33F430FB007E811DF101B03A" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_A53DBA8B397F1824E2B6811DF0FF8B3C" xlink:to="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsIncludingGoodwill_EFF321BD33F430FB007E811DF101B03A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_70FE247912696F3982A4811DF1010BEC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8E8F26D2FC845AFACCE1811DF0FF99C5" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_70FE247912696F3982A4811DF1010BEC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_34B807ACE222EC693C4F811DF101E840" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_70FE247912696F3982A4811DF1010BEC" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_34B807ACE222EC693C4F811DF101E840" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther_C25EBC9F1D5215C8DA38811DF102C60C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_70FE247912696F3982A4811DF1010BEC" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther_C25EBC9F1D5215C8DA38811DF102C60C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilitiesCurrent" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilitiesCurrent_270503052C2074389D38811DF102F976" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_70FE247912696F3982A4811DF1010BEC" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilitiesCurrent_270503052C2074389D38811DF102F976" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilitiesNoncurrent" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilitiesNoncurrent_8B4DD9EB7E92019DF2D1811DF102C497" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_70FE247912696F3982A4811DF1010BEC" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilitiesNoncurrent_8B4DD9EB7E92019DF2D1811DF102C497" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_1693E3E14DC59EAE32B9811DF102D5BD" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_70FE247912696F3982A4811DF1010BEC" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_1693E3E14DC59EAE32B9811DF102D5BD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_771911BC4754E1D99C5D811DF1030B3A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8E8F26D2FC845AFACCE1811DF0FF99C5" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_771911BC4754E1D99C5D811DF1030B3A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashAcquiredFromAcquisition" xlink:label="loc_us-gaap_CashAcquiredFromAcquisition_3312451A35D804DE8F40811E2E62B10E" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8E8F26D2FC845AFACCE1811DF0FF99C5" xlink:to="loc_us-gaap_CashAcquiredFromAcquisition_3312451A35D804DE8F40811E2E62B10E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/AcquisitionsSummaryOfUnauditedConsolidatedResultsOfOperationsIncludingProformaResultsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/AcquisitionsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/CommitmentsAndContingencies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/CommitmentsAndContingenciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherCommitmentsLineItems" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_0919956D429E16F560098173C7CDB544" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherCommitmentsTable" xlink:label="loc_us-gaap_OtherCommitmentsTable_CE0FB74D7266D5D053128173C7CCF36E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_0919956D429E16F560098173C7CDB544" xlink:to="loc_us-gaap_OtherCommitmentsTable_CE0FB74D7266D5D053128173C7CCF36E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_7973F1792790EBA9E6F18173C7CC6FEB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_CE0FB74D7266D5D053128173C7CCF36E" xlink:to="loc_us-gaap_RangeAxis_7973F1792790EBA9E6F18173C7CC6FEB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_C91E9637034A2FFAE9498173C7CCA681_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_7973F1792790EBA9E6F18173C7CC6FEB" xlink:to="loc_us-gaap_RangeMember_C91E9637034A2FFAE9498173C7CCA681_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_C91E9637034A2FFAE9498173C7CCA681" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_7973F1792790EBA9E6F18173C7CC6FEB" xlink:to="loc_us-gaap_RangeMember_C91E9637034A2FFAE9498173C7CCA681" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_7896C1CB13CCAD80C2778173C7CC1EA5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_C91E9637034A2FFAE9498173C7CCA681" xlink:to="loc_us-gaap_MinimumMember_7896C1CB13CCAD80C2778173C7CC1EA5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_0720C5DC64B3A29D7B788173C7CC0CB1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_C91E9637034A2FFAE9498173C7CCA681" xlink:to="loc_us-gaap_MaximumMember_0720C5DC64B3A29D7B788173C7CC0CB1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LeaseAndRentalExpense" xlink:label="loc_us-gaap_LeaseAndRentalExpense_E66DC707C992EC0DCDDB8173C7CDA70D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_0919956D429E16F560098173C7CDB544" xlink:to="loc_us-gaap_LeaseAndRentalExpense_E66DC707C992EC0DCDDB8173C7CDA70D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SaleLeasebackTransactionGrossProceedsInvestingActivities" xlink:label="loc_us-gaap_SaleLeasebackTransactionGrossProceedsInvestingActivities_981E1C9E35A834F079B98173C7CD6A2F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_0919956D429E16F560098173C7CDB544" xlink:to="loc_us-gaap_SaleLeasebackTransactionGrossProceedsInvestingActivities_981E1C9E35A834F079B98173C7CD6A2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LesseeLeasingArrangementsOperatingLeasesTermOfContract" xlink:label="loc_us-gaap_LesseeLeasingArrangementsOperatingLeasesTermOfContract_7634498FEF4E8F98DB4F8173C7CECDE6" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_0919956D429E16F560098173C7CDB544" xlink:to="loc_us-gaap_LesseeLeasingArrangementsOperatingLeasesTermOfContract_7634498FEF4E8F98DB4F8173C7CECDE6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredCreditsAndOtherLiabilities" xlink:label="loc_us-gaap_DeferredCreditsAndOtherLiabilities_DBFC10FCF1C45BBA2DF98173C7CEFEFE" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_0919956D429E16F560098173C7CDB544" xlink:to="loc_us-gaap_DeferredCreditsAndOtherLiabilities_DBFC10FCF1C45BBA2DF98173C7CEFEFE" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_DecreaseinOperatingExpenseGrantsforPropertyPlantandEquipment" xlink:label="loc_mmsi_DecreaseinOperatingExpenseGrantsforPropertyPlantandEquipment_D1D3555E5FEBF15688E68173C7CE563B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_0919956D429E16F560098173C7CDB544" xlink:to="loc_mmsi_DecreaseinOperatingExpenseGrantsforPropertyPlantandEquipment_D1D3555E5FEBF15688E68173C7CE563B" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_OtherCommitmentForeignGovernmentGrantLiabilityPeriod" xlink:label="loc_mmsi_OtherCommitmentForeignGovernmentGrantLiabilityPeriod_BB91D1C114FA094E81A18173C7CE5EB9" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_0919956D429E16F560098173C7CDB544" xlink:to="loc_mmsi_OtherCommitmentForeignGovernmentGrantLiabilityPeriod_BB91D1C114FA094E81A18173C7CE5EB9" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_GrantRefundableforDiscontinuedOperations" xlink:label="loc_mmsi_GrantRefundableforDiscontinuedOperations_1B69B2A2CF488DCD1AD88173C7CEA30B" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_0919956D429E16F560098173C7CDB544" xlink:to="loc_mmsi_GrantRefundableforDiscontinuedOperations_1B69B2A2CF488DCD1AD88173C7CEA30B" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_OtherCommitmentForeignGovernmentGrantLiabilityRemainingPeriod" xlink:label="loc_mmsi_OtherCommitmentForeignGovernmentGrantLiabilityRemainingPeriod_58C99604BB6F893DBA348173C7CEEBF2" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_0919956D429E16F560098173C7CDB544" xlink:to="loc_mmsi_OtherCommitmentForeignGovernmentGrantLiabilityRemainingPeriod_58C99604BB6F893DBA348173C7CEEBF2" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/CommitmentsAndContingenciesScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/CommitmentsAndContingenciesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/ConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_9C90087F47475C5545198105CC89473A" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_F51E007C23F317C221118105CC87F4A7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_9C90087F47475C5545198105CC89473A" xlink:to="loc_us-gaap_StatementTable_F51E007C23F317C221118105CC87F4A7" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_67A33C2F850668863FEE8105CC88A980" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_F51E007C23F317C221118105CC87F4A7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_67A33C2F850668863FEE8105CC88A980" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_395DDF64A45599BB78E38105CC885899_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_67A33C2F850668863FEE8105CC88A980" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_395DDF64A45599BB78E38105CC885899_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_395DDF64A45599BB78E38105CC885899" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_67A33C2F850668863FEE8105CC88A980" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_395DDF64A45599BB78E38105CC885899" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_69E8FF2F5F710008F0968105CC88E8D3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_395DDF64A45599BB78E38105CC885899" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_69E8FF2F5F710008F0968105CC88E8D3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_16CB2BDC8FECCC78284D8105CC88CF37" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_395DDF64A45599BB78E38105CC885899" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_16CB2BDC8FECCC78284D8105CC88CF37" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaap_AssetsAbstract_4DC1638CCBAD44BA88458105CC891585" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9C90087F47475C5545198105CC89473A" xlink:to="loc_us-gaap_AssetsAbstract_4DC1638CCBAD44BA88458105CC891585" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="loc_us-gaap_AssetsCurrentAbstract_57F5A4D631761C8E61958105CC89825A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4DC1638CCBAD44BA88458105CC891585" xlink:to="loc_us-gaap_AssetsCurrentAbstract_57F5A4D631761C8E61958105CC89825A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_6024A712F23598B2F6F98105CC89C104" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_57F5A4D631761C8E61958105CC89825A" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_6024A712F23598B2F6F98105CC89C104" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_E11832D4D906839077768105CC89D60A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_57F5A4D631761C8E61958105CC89825A" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_E11832D4D906839077768105CC89D60A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DueFromEmployeesCurrent" xlink:label="loc_us-gaap_DueFromEmployeesCurrent_1A2BC8E9B35F4AA764338105CC89E315" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_57F5A4D631761C8E61958105CC89825A" xlink:to="loc_us-gaap_DueFromEmployeesCurrent_1A2BC8E9B35F4AA764338105CC89E315" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NontradeReceivablesCurrent" xlink:label="loc_us-gaap_NontradeReceivablesCurrent_3CBB2F1885797781DBB28105CC89BF05" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_57F5A4D631761C8E61958105CC89825A" xlink:to="loc_us-gaap_NontradeReceivablesCurrent_3CBB2F1885797781DBB28105CC89BF05" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_InventoryNet" xlink:label="loc_us-gaap_InventoryNet_06AEE816E17689B88D4D8105CC8A8DF2" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_57F5A4D631761C8E61958105CC89825A" xlink:to="loc_us-gaap_InventoryNet_06AEE816E17689B88D4D8105CC8A8DF2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_0F5FCE973960531761A48105CC8A61D9" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_57F5A4D631761C8E61958105CC89825A" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_0F5FCE973960531761A48105CC8A61D9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PrepaidTaxes" xlink:label="loc_us-gaap_PrepaidTaxes_B32B2B21D0374CD9BB278105CC8A60FA" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_57F5A4D631761C8E61958105CC89825A" xlink:to="loc_us-gaap_PrepaidTaxes_B32B2B21D0374CD9BB278105CC8A60FA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredTaxAssetsNetCurrent" xlink:label="loc_us-gaap_DeferredTaxAssetsNetCurrent_2ADB817EBFA85EAD45EB8105CC8A8EC9" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_57F5A4D631761C8E61958105CC89825A" xlink:to="loc_us-gaap_DeferredTaxAssetsNetCurrent_2ADB817EBFA85EAD45EB8105CC8A8EC9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeTaxesReceivable" xlink:label="loc_us-gaap_IncomeTaxesReceivable_C63F5F9280EA643776DC8105CC8A172A" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_57F5A4D631761C8E61958105CC89825A" xlink:to="loc_us-gaap_IncomeTaxesReceivable_C63F5F9280EA643776DC8105CC8A172A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaap_AssetsCurrent_404FA7E9498C795080FB8105CC8AE5A0" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_57F5A4D631761C8E61958105CC89825A" xlink:to="loc_us-gaap_AssetsCurrent_404FA7E9498C795080FB8105CC8AE5A0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNetAbstract" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_8E8CFB24350A3954427C8105CC8AC81B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4DC1638CCBAD44BA88458105CC891585" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_8E8CFB24350A3954427C8105CC8AC81B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Land" xlink:label="loc_us-gaap_Land_8F728CBA4B768904D6A48105CC8B96FB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_8E8CFB24350A3954427C8105CC8AC81B" xlink:to="loc_us-gaap_Land_8F728CBA4B768904D6A48105CC8B96FB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BuildingsAndImprovementsGross" xlink:label="loc_us-gaap_BuildingsAndImprovementsGross_6022E82C0DAEC6BD535F8105CC8B9939" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_8E8CFB24350A3954427C8105CC8AC81B" xlink:to="loc_us-gaap_BuildingsAndImprovementsGross_6022E82C0DAEC6BD535F8105CC8B9939" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MachineryAndEquipmentGross" xlink:label="loc_us-gaap_MachineryAndEquipmentGross_FA556319A30FD6564D9E8105CC8B22CF" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_8E8CFB24350A3954427C8105CC8AC81B" xlink:to="loc_us-gaap_MachineryAndEquipmentGross_FA556319A30FD6564D9E8105CC8B22CF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FurnitureAndFixturesGross" xlink:label="loc_us-gaap_FurnitureAndFixturesGross_7415196C1EF0D1596E8E8105CC8B9E03" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_8E8CFB24350A3954427C8105CC8AC81B" xlink:to="loc_us-gaap_FurnitureAndFixturesGross_7415196C1EF0D1596E8E8105CC8B9E03" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LeaseholdImprovementsGross" xlink:label="loc_us-gaap_LeaseholdImprovementsGross_8F4C54DA42FD753239038105CC8BC161" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_8E8CFB24350A3954427C8105CC8AC81B" xlink:to="loc_us-gaap_LeaseholdImprovementsGross_8F4C54DA42FD753239038105CC8BC161" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConstructionInProgressGross" xlink:label="loc_us-gaap_ConstructionInProgressGross_C931342136DBD69E9A458105CC8B7AD4" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_8E8CFB24350A3954427C8105CC8AC81B" xlink:to="loc_us-gaap_ConstructionInProgressGross_C931342136DBD69E9A458105CC8B7AD4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_869F0D78AC4B11CB43188105CC8BD2F5" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_8E8CFB24350A3954427C8105CC8AC81B" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_869F0D78AC4B11CB43188105CC8BD2F5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_4AAA84B111F28C6A7F488105CC8BD861" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_8E8CFB24350A3954427C8105CC8AC81B" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_4AAA84B111F28C6A7F488105CC8BD861" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_368DDCC397F82275EF018105CC8CE538" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNetAbstract_8E8CFB24350A3954427C8105CC8AC81B" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_368DDCC397F82275EF018105CC8CE538" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrentAbstract" xlink:label="loc_mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrentAbstract_F172523AF1248C24AAAA8105CC8C2A6A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4DC1638CCBAD44BA88458105CC891585" xlink:to="loc_mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrentAbstract_F172523AF1248C24AAAA8105CC8C2A6A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_2816F9C84795950CCCC68105CC8C9DE3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrentAbstract_F172523AF1248C24AAAA8105CC8C2A6A" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_2816F9C84795950CCCC68105CC8C9DE3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_4E174EEEFDA0DE72E79F8105CC8C7068" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrentAbstract_F172523AF1248C24AAAA8105CC8C2A6A" xlink:to="loc_us-gaap_Goodwill_4E174EEEFDA0DE72E79F8105CC8C7068" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredTaxAssetsNetNoncurrent" xlink:label="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_C5C48CCE13FE7B3C3CFA8105CC8C0395" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrentAbstract_F172523AF1248C24AAAA8105CC8C2A6A" xlink:to="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_C5C48CCE13FE7B3C3CFA8105CC8C0395" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_2CCDD03FAF169775F0B88105CC8C41B0" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrentAbstract_F172523AF1248C24AAAA8105CC8C2A6A" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_2CCDD03FAF169775F0B88105CC8C41B0" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrent" xlink:label="loc_mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrent_FE2A76875D6A6BD7B92C8105CC8C0555" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrentAbstract_F172523AF1248C24AAAA8105CC8C2A6A" xlink:to="loc_mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrent_FE2A76875D6A6BD7B92C8105CC8C0555" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_E605A050119677C641408105CC8D82AD" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4DC1638CCBAD44BA88458105CC891585" xlink:to="loc_us-gaap_Assets_E605A050119677C641408105CC8D82AD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9C90087F47475C5545198105CC89473A" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_AAA2B6DE9E093B68E4A98105CC8DC194" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_AAA2B6DE9E093B68E4A98105CC8DC194" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccountsPayableTradeCurrent" xlink:label="loc_us-gaap_AccountsPayableTradeCurrent_5B5661D501A65F34B6B38105CC8D90CC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_AAA2B6DE9E093B68E4A98105CC8DC194" xlink:to="loc_us-gaap_AccountsPayableTradeCurrent_5B5661D501A65F34B6B38105CC8D90CC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_0C7AC4817146674A210E8105CC8D443E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_AAA2B6DE9E093B68E4A98105CC8DC194" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_0C7AC4817146674A210E8105CC8D443E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="loc_us-gaap_LongTermDebtCurrent_76EF5DA856642A73104E8105CC8D28EB" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_AAA2B6DE9E093B68E4A98105CC8DC194" xlink:to="loc_us-gaap_LongTermDebtCurrent_76EF5DA856642A73104E8105CC8D28EB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DueToEmployeesCurrent" xlink:label="loc_us-gaap_DueToEmployeesCurrent_0774C5D080F1B6F424368105CC8DC2AC" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_AAA2B6DE9E093B68E4A98105CC8DC194" xlink:to="loc_us-gaap_DueToEmployeesCurrent_0774C5D080F1B6F424368105CC8DC2AC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccruedIncomeTaxesCurrent" xlink:label="loc_us-gaap_AccruedIncomeTaxesCurrent_B90E8FFDAAB5F741803D8105CC8EC9AA" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_AAA2B6DE9E093B68E4A98105CC8DC194" xlink:to="loc_us-gaap_AccruedIncomeTaxesCurrent_B90E8FFDAAB5F741803D8105CC8EC9AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="loc_us-gaap_LiabilitiesCurrent_F0F929D23833C534AECB8105CC8E0607" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_AAA2B6DE9E093B68E4A98105CC8DC194" xlink:to="loc_us-gaap_LiabilitiesCurrent_F0F929D23833C534AECB8105CC8E0607" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_7FD86375EF1B37E727178105CC8E3BE2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_7FD86375EF1B37E727178105CC8E3BE2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredTaxLiabilitiesNoncurrent" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesNoncurrent_DDB13301C282532A9CAC8105CC8E82D4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesNoncurrent_DDB13301C282532A9CAC8105CC8E82D4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilityForUncertainTaxPositionsNoncurrent" xlink:label="loc_us-gaap_LiabilityForUncertainTaxPositionsNoncurrent_5CACB1C00FA3940E289D8105CC8E2C9F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:to="loc_us-gaap_LiabilityForUncertainTaxPositionsNoncurrent_5CACB1C00FA3940E289D8105CC8E2C9F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredCompensationLiabilityClassifiedNoncurrent" xlink:label="loc_us-gaap_DeferredCompensationLiabilityClassifiedNoncurrent_0179FE750EABECF1B48C8105CC8E0552" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:to="loc_us-gaap_DeferredCompensationLiabilityClassifiedNoncurrent_0179FE750EABECF1B48C8105CC8E0552" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherDeferredCreditsNoncurrent" xlink:label="loc_us-gaap_OtherDeferredCreditsNoncurrent_83ABF56655FBB863520A8105CC8E4D97" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:to="loc_us-gaap_OtherDeferredCreditsNoncurrent_83ABF56655FBB863520A8105CC8E4D97" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_9B9E0551822233616CBD8105CC8FA8B1" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_9B9E0551822233616CBD8105CC8FA8B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Liabilities" xlink:label="loc_us-gaap_Liabilities_3275173707654807EA738105CC8F7E8F" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:to="loc_us-gaap_Liabilities_3275173707654807EA738105CC8F7E8F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="loc_us-gaap_CommitmentsAndContingencies_5BC36051CF73FBED3E658105CC8F3566" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:to="loc_us-gaap_CommitmentsAndContingencies_5BC36051CF73FBED3E658105CC8F3566" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5EE745268703D68546A28105CC8F2334" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5EE745268703D68546A28105CC8F2334" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PreferredStockValue" xlink:label="loc_us-gaap_PreferredStockValue_26BD2F55F0FBAD0AFACF8105CC8FFD66" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5EE745268703D68546A28105CC8F2334" xlink:to="loc_us-gaap_PreferredStockValue_26BD2F55F0FBAD0AFACF8105CC8FFD66" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockValue" xlink:label="loc_us-gaap_CommonStockValue_1768A5ECA986F7E4F06F8105CC8F56BB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5EE745268703D68546A28105CC8F2334" xlink:to="loc_us-gaap_CommonStockValue_1768A5ECA986F7E4F06F8105CC8F56BB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_385B61DD3DB270F942DA8105CC8F6D5C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5EE745268703D68546A28105CC8F2334" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_385B61DD3DB270F942DA8105CC8F6D5C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_96FAC83555709C04218D8105CC90ECFC" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5EE745268703D68546A28105CC8F2334" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_96FAC83555709C04218D8105CC90ECFC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_9113D43D28D555074D368105CC90825B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5EE745268703D68546A28105CC8F2334" xlink:to="loc_us-gaap_StockholdersEquity_9113D43D28D555074D368105CC90825B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_22404B44111CB81FAA518105CC90E71A" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_DC0045527B87DE84CE058105CC8D2BFA" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_22404B44111CB81FAA518105CC90E71A" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_EA34BFBFEC21661AFF0047FDCB07D0E0" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_E1ACBE0E7E4161AFBE7E47FDCB06F699" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_EA34BFBFEC21661AFF0047FDCB07D0E0" xlink:to="loc_us-gaap_StatementTable_E1ACBE0E7E4161AFBE7E47FDCB06F699" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_8944293FD0DB14D1679347FDCB06FBAF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_E1ACBE0E7E4161AFBE7E47FDCB06F699" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_8944293FD0DB14D1679347FDCB06FBAF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1A576BD3A2ECD2883FBE47FDCB06A361_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_8944293FD0DB14D1679347FDCB06FBAF" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1A576BD3A2ECD2883FBE47FDCB06A361_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1A576BD3A2ECD2883FBE47FDCB06A361" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_8944293FD0DB14D1679347FDCB06FBAF" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1A576BD3A2ECD2883FBE47FDCB06A361" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_708D1FFB42AFFD1BF88147FDCB065E14" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1A576BD3A2ECD2883FBE47FDCB06A361" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_708D1FFB42AFFD1BF88147FDCB065E14" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_2C22B7939B48AB2C485E47FDCB061DF5" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1A576BD3A2ECD2883FBE47FDCB06A361" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_2C22B7939B48AB2C485E47FDCB061DF5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="loc_us-gaap_AssetsCurrentAbstract_AE31954CB14571A1F1E447FDCB077628" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_EA34BFBFEC21661AFF0047FDCB07D0E0" xlink:to="loc_us-gaap_AssetsCurrentAbstract_AE31954CB14571A1F1E447FDCB077628" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_0D15FFE7B35C5E3B193947FDCB079C83" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_AE31954CB14571A1F1E447FDCB077628" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_0D15FFE7B35C5E3B193947FDCB079C83" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrentAbstract" xlink:label="loc_mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrentAbstract_7B92415CF49BA72C41B647FDCB078B04" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_EA34BFBFEC21661AFF0047FDCB07D0E0" xlink:to="loc_mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrentAbstract_7B92415CF49BA72C41B647FDCB078B04" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_29BDDFE7FBECDD38ADEE47FDCB080BBF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_IntangibleAssetsNetGoodwillAndOtherAssetsNoncurrentAbstract_7B92415CF49BA72C41B647FDCB078B04" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_29BDDFE7FBECDD38ADEE47FDCB080BBF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_F95008E73225F0EDBDAB47FDCB08D32C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_EA34BFBFEC21661AFF0047FDCB07D0E0" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_F95008E73225F0EDBDAB47FDCB08D32C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_FA1A48CA1179980D8EB447FDCB0877B3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_F95008E73225F0EDBDAB47FDCB08D32C" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_FA1A48CA1179980D8EB447FDCB0877B3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="loc_us-gaap_PreferredStockSharesIssued_609E99D4F2247458EFD047FDCB08D116" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_F95008E73225F0EDBDAB47FDCB08D32C" xlink:to="loc_us-gaap_PreferredStockSharesIssued_609E99D4F2247458EFD047FDCB08D116" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_10B5CF09723A5A62898D47FDCB082ECE" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_F95008E73225F0EDBDAB47FDCB08D32C" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_10B5CF09723A5A62898D47FDCB082ECE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_70C74493E41043E9122747FDCB087D71" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_F95008E73225F0EDBDAB47FDCB08D32C" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_70C74493E41043E9122747FDCB087D71" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="loc_us-gaap_CommonStockSharesIssued_1C11253C8DBE4EF36B4547FDCB0929C3" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_F95008E73225F0EDBDAB47FDCB08D32C" xlink:to="loc_us-gaap_CommonStockSharesIssued_1C11253C8DBE4EF36B4547FDCB0929C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_FCD85AB10829EDED857D47FDCB09F862" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_F95008E73225F0EDBDAB47FDCB08D32C" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_FCD85AB10829EDED857D47FDCB09F862" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/ConsolidatedStatementsOfCashFlows" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/ConsolidatedStatementsOfCashFlowsParenthetical" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_CE2429680BB39BDB3666D27CCA170A56" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_329EDB3FA32DB08B76E0D27CCA17839F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_CE2429680BB39BDB3666D27CCA170A56" xlink:to="loc_us-gaap_StatementTable_329EDB3FA32DB08B76E0D27CCA17839F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_D724632DFF7952E02355D27CCA1795F4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_329EDB3FA32DB08B76E0D27CCA17839F" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_D724632DFF7952E02355D27CCA1795F4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_58521B2D5DFD81113C1ED27CCA170DE0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_D724632DFF7952E02355D27CCA1795F4" xlink:to="loc_us-gaap_EquityComponentDomain_58521B2D5DFD81113C1ED27CCA170DE0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_58521B2D5DFD81113C1ED27CCA170DE0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_D724632DFF7952E02355D27CCA1795F4" xlink:to="loc_us-gaap_EquityComponentDomain_58521B2D5DFD81113C1ED27CCA170DE0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_1377F35BE2633698E45CD27CCA17F40A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_58521B2D5DFD81113C1ED27CCA170DE0" xlink:to="loc_us-gaap_CommonStockMember_1377F35BE2633698E45CD27CCA17F40A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_InterestPaidCapitalized" xlink:label="loc_us-gaap_InterestPaidCapitalized_8D619149391ABC41ECABD27CCA177772" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_CE2429680BB39BDB3666D27CCA170A56" xlink:to="loc_us-gaap_InterestPaidCapitalized_8D619149391ABC41ECABD27CCA177772" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_StockSurrenderedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_mmsi_StockSurrenderedDuringPeriodSharesStockOptionsExercised_46D81D45F0FA0DFB362AD27CCA17AE37" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_CE2429680BB39BDB3666D27CCA170A56" xlink:to="loc_mmsi_StockSurrenderedDuringPeriodSharesStockOptionsExercised_46D81D45F0FA0DFB362AD27CCA17AE37" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/ConsolidatedStatementsOfComprehensiveIncome" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/ConsolidatedStatementsOfOperations" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/ConsolidatedStatementsOfStockholdersEquity" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_E3BB742E49600E9C2E278105CC4E8AE7" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_A1678CD0FA31D349D2558105CC4C7F99" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_E3BB742E49600E9C2E278105CC4E8AE7" xlink:to="loc_us-gaap_StatementTable_A1678CD0FA31D349D2558105CC4C7F99" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_6C69E1E9B514796812608105CC4D19D0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_A1678CD0FA31D349D2558105CC4C7F99" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_6C69E1E9B514796812608105CC4D19D0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_907396A364A85677010B8105CC4DB474_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_6C69E1E9B514796812608105CC4D19D0" xlink:to="loc_us-gaap_EquityComponentDomain_907396A364A85677010B8105CC4DB474_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_907396A364A85677010B8105CC4DB474" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_6C69E1E9B514796812608105CC4D19D0" xlink:to="loc_us-gaap_EquityComponentDomain_907396A364A85677010B8105CC4DB474" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_052F7FC446F1B8BC3DE78105CC4D9295" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_907396A364A85677010B8105CC4DB474" xlink:to="loc_us-gaap_CommonStockMember_052F7FC446F1B8BC3DE78105CC4D9295" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember_533649A4EE54D01407528105CC4EBD54" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_907396A364A85677010B8105CC4DB474" xlink:to="loc_us-gaap_RetainedEarningsMember_533649A4EE54D01407528105CC4EBD54" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_B5386F77C1A6EA390FBC8105CC4EF0D9" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_907396A364A85677010B8105CC4DB474" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_B5386F77C1A6EA390FBC8105CC4EF0D9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E3BB742E49600E9C2E278105CC4E8AE7" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_2072101079235676511F8105CC4FE229" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_us-gaap_StockholdersEquity_2072101079235676511F8105CC4FE229" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_3267C4785A62F44F549F8105CC4FE23B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_3267C4785A62F44F549F8105CC4FE23B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_C713CC2F83E398A299F08105CC4F4DA7" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_us-gaap_NetIncomeLoss_C713CC2F83E398A299F08105CC4F4DA7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_DE89463BD0C2768BD5478105CC4FD226" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_DE89463BD0C2768BD5478105CC4FD226" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalTaxEffectFromShareBasedCompensation" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalTaxEffectFromShareBasedCompensation_6433A98C3EC6B412FCFD8105CC4F2E3E" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalTaxEffectFromShareBasedCompensation_6433A98C3EC6B412FCFD8105CC4F2E3E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_AB602422BFA86473B0F48105CC4F808F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_AB602422BFA86473B0F48105CC4F808F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_E8AD31BD8A81860C13368105CC4F7499" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_E8AD31BD8A81860C13368105CC4F7499" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_6F404C7BEB5449EEF48B8105CC4FA631" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_6F404C7BEB5449EEF48B8105CC4FA631" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_CC43A0FED491969FB7378105CC5096A7" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_CC43A0FED491969FB7378105CC5096A7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_4398B2C65B0AA52506E08105CC51C83A" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_4398B2C65B0AA52506E08105CC51C83A" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_StockSurrenderedDuringPeriodValuePayrollTaxLiabilitiesStockOptionsExercised" xlink:label="loc_mmsi_StockSurrenderedDuringPeriodValuePayrollTaxLiabilitiesStockOptionsExercised_4CA9D1E7147FF607047E8105CC51D8AE" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_mmsi_StockSurrenderedDuringPeriodValuePayrollTaxLiabilitiesStockOptionsExercised_4CA9D1E7147FF607047E8105CC51D8AE" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_StockSurrenderedDuringPeriodSharesPayrollTaxLiabilitiesStockOptionsExercised" xlink:label="loc_mmsi_StockSurrenderedDuringPeriodSharesPayrollTaxLiabilitiesStockOptionsExercised_E213597B4F2A91692C0B8105CC511F8C" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_mmsi_StockSurrenderedDuringPeriodSharesPayrollTaxLiabilitiesStockOptionsExercised_E213597B4F2A91692C0B8105CC511F8C" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_StockSurrenderedDuringPeriodValueStockOptionsExercised" xlink:label="loc_mmsi_StockSurrenderedDuringPeriodValueStockOptionsExercised_645DFE38B28F9FBC49278105CC51D764" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_mmsi_StockSurrenderedDuringPeriodValueStockOptionsExercised_645DFE38B28F9FBC49278105CC51D764" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_StockSurrenderedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_mmsi_StockSurrenderedDuringPeriodSharesStockOptionsExercised_5BCC5103FD1A87E6BBB28105CC51AFF3" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_368F254B76A70436321E8105CC4EF587" xlink:to="loc_mmsi_StockSurrenderedDuringPeriodSharesStockOptionsExercised_5BCC5103FD1A87E6BBB28105CC51AFF3" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/Derivatives" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/DerivativesAmountOfGainLossRecognizedInOciAndIncomeStatementDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_A1E05570A6C429251FBA80C027640378" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_6C6AC7B7B9AC613B844480C027639174" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_A1E05570A6C429251FBA80C027640378" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_6C6AC7B7B9AC613B844480C027639174" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_7ED67DB5F6CA375BD29680C027639950" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_6C6AC7B7B9AC613B844480C027639174" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_7ED67DB5F6CA375BD29680C027639950" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="loc_us-gaap_HedgingRelationshipDomain_C0C923D872CA63AA030180C02763C86E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_7ED67DB5F6CA375BD29680C027639950" xlink:to="loc_us-gaap_HedgingRelationshipDomain_C0C923D872CA63AA030180C02763C86E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="loc_us-gaap_HedgingRelationshipDomain_C0C923D872CA63AA030180C02763C86E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_7ED67DB5F6CA375BD29680C027639950" xlink:to="loc_us-gaap_HedgingRelationshipDomain_C0C923D872CA63AA030180C02763C86E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashFlowHedgingMember" xlink:label="loc_us-gaap_CashFlowHedgingMember_71622591A0D214678B8780C02763C3C6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_C0C923D872CA63AA030180C02763C86E" xlink:to="loc_us-gaap_CashFlowHedgingMember_71622591A0D214678B8780C02763C3C6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_F4CF2A24F21D20CD3E3F80C02763CC0F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_6C6AC7B7B9AC613B844480C027639174" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_F4CF2A24F21D20CD3E3F80C02763CC0F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_75E92B62CAB3B2A2A96980C0276340A5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_F4CF2A24F21D20CD3E3F80C02763CC0F" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_75E92B62CAB3B2A2A96980C0276340A5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_75E92B62CAB3B2A2A96980C0276340A5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_F4CF2A24F21D20CD3E3F80C02763CC0F" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_75E92B62CAB3B2A2A96980C0276340A5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_InterestRateSwapMember" xlink:label="loc_us-gaap_InterestRateSwapMember_50764B2D44CD7E5DFFFE80C02763BEB6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_75E92B62CAB3B2A2A96980C0276340A5" xlink:to="loc_us-gaap_InterestRateSwapMember_50764B2D44CD7E5DFFFE80C02763BEB6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ForeignExchangeForwardMember" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_B980FAFB1C0448F9042880D78E4BD913" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_75E92B62CAB3B2A2A96980C0276340A5" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_B980FAFB1C0448F9042880D78E4BD913" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_91258FE05BD2BEC9823580C027633820" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_6C6AC7B7B9AC613B844480C027639174" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_91258FE05BD2BEC9823580C027633820" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_13947F7617EABEEFB1A280C027630D1C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_91258FE05BD2BEC9823580C027633820" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_13947F7617EABEEFB1A280C027630D1C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_13947F7617EABEEFB1A280C027630D1C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_91258FE05BD2BEC9823580C027633820" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_13947F7617EABEEFB1A280C027630D1C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_InterestExpenseMember" xlink:label="loc_us-gaap_InterestExpenseMember_1DEA7423A1AEEFC5885E80C02763D0BB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_13947F7617EABEEFB1A280C027630D1C" xlink:to="loc_us-gaap_InterestExpenseMember_1DEA7423A1AEEFC5885E80C02763D0BB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SalesRevenueNetMember" xlink:label="loc_us-gaap_SalesRevenueNetMember_53B72EC13E6CAA59E26780C027641358" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_13947F7617EABEEFB1A280C027630D1C" xlink:to="loc_us-gaap_SalesRevenueNetMember_53B72EC13E6CAA59E26780C027641358" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CostOfGoodsTotalMember" xlink:label="loc_us-gaap_CostOfGoodsTotalMember_E1052B56499443C3AA5B80C027643E99" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_13947F7617EABEEFB1A280C027630D1C" xlink:to="loc_us-gaap_CostOfGoodsTotalMember_E1052B56499443C3AA5B80C027643E99" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet_7F7E8068334E8598522F80C027644005" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_A1E05570A6C429251FBA80C027640378" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet_7F7E8068334E8598522F80C027644005" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet_0D6C60E75B292F5EB0BA80C02764BBAA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_A1E05570A6C429251FBA80C027640378" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet_0D6C60E75B292F5EB0BA80C02764BBAA" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/DerivativesFairValueOfDerivativeInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativesFairValueLineItems" xlink:label="loc_us-gaap_DerivativesFairValueLineItems_DC217AE30D3FF3765EA580C0276A4774" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:label="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_12982DE4A4331955FAA880C02768B3EF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_DC217AE30D3FF3765EA580C0276A4774" xlink:to="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_12982DE4A4331955FAA880C02768B3EF" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingDesignationAxis" xlink:label="loc_us-gaap_HedgingDesignationAxis_4493D11A9D8103D8889880C02769B80E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_12982DE4A4331955FAA880C02768B3EF" xlink:to="loc_us-gaap_HedgingDesignationAxis_4493D11A9D8103D8889880C02769B80E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="loc_us-gaap_HedgingDesignationDomain_0BEBA7F2EEE602F07EB680C02769D037_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_4493D11A9D8103D8889880C02769B80E" xlink:to="loc_us-gaap_HedgingDesignationDomain_0BEBA7F2EEE602F07EB680C02769D037_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="loc_us-gaap_HedgingDesignationDomain_0BEBA7F2EEE602F07EB680C02769D037" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_4493D11A9D8103D8889880C02769B80E" xlink:to="loc_us-gaap_HedgingDesignationDomain_0BEBA7F2EEE602F07EB680C02769D037" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DesignatedAsHedgingInstrumentMember" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_CE6AF2C78702D92325AA80C02769E467" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_0BEBA7F2EEE602F07EB680C02769D037" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_CE6AF2C78702D92325AA80C02769E467" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NondesignatedMember" xlink:label="loc_us-gaap_NondesignatedMember_5027E4BE52EFC11100AD80C02769AE40" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_0BEBA7F2EEE602F07EB680C02769D037" xlink:to="loc_us-gaap_NondesignatedMember_5027E4BE52EFC11100AD80C02769AE40" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_B39B3A39F2AAE3FF953880C02769A1DD" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_12982DE4A4331955FAA880C02768B3EF" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_B39B3A39F2AAE3FF953880C02769A1DD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_E7B95E9352422FDC0E6280C02769BE58_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_B39B3A39F2AAE3FF953880C02769A1DD" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_E7B95E9352422FDC0E6280C02769BE58_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_E7B95E9352422FDC0E6280C02769BE58" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_B39B3A39F2AAE3FF953880C02769A1DD" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_E7B95E9352422FDC0E6280C02769BE58" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_InterestRateSwapMember" xlink:label="loc_us-gaap_InterestRateSwapMember_BD49615322571579978E80C02769A268" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_E7B95E9352422FDC0E6280C02769BE58" xlink:to="loc_us-gaap_InterestRateSwapMember_BD49615322571579978E80C02769A268" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ForeignExchangeForwardMember" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_1AB2552297EB54CB467A80D388520EFE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_E7B95E9352422FDC0E6280C02769BE58" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_1AB2552297EB54CB467A80D388520EFE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_90805EE0B5C05C99482380C0276901F3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_12982DE4A4331955FAA880C02768B3EF" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_90805EE0B5C05C99482380C0276901F3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_383A297A17EBAC97454780C02769F426_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_90805EE0B5C05C99482380C0276901F3" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_383A297A17EBAC97454780C02769F426_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_383A297A17EBAC97454780C02769F426" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_90805EE0B5C05C99482380C0276901F3" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_383A297A17EBAC97454780C02769F426" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherNoncurrentAssetsMember" xlink:label="loc_us-gaap_OtherNoncurrentAssetsMember_DBAC404C4BAFCDFA609B80C027693195" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_383A297A17EBAC97454780C02769F426" xlink:to="loc_us-gaap_OtherNoncurrentAssetsMember_DBAC404C4BAFCDFA609B80C027693195" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember" xlink:label="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_508B7391BE7DAA1728E280C02769E6BF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_383A297A17EBAC97454780C02769F426" xlink:to="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_508B7391BE7DAA1728E280C02769E6BF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccruedLiabilitiesMember" xlink:label="loc_us-gaap_AccruedLiabilitiesMember_C68DBC366D0EA7E5BC5E80C0276A513B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_383A297A17EBAC97454780C02769F426" xlink:to="loc_us-gaap_AccruedLiabilitiesMember_C68DBC366D0EA7E5BC5E80C0276A513B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherNoncurrentLiabilitiesMember" xlink:label="loc_us-gaap_OtherNoncurrentLiabilitiesMember_BA1E8940226C090ABE6D80D5A96B99E4" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_383A297A17EBAC97454780C02769F426" xlink:to="loc_us-gaap_OtherNoncurrentLiabilitiesMember_BA1E8940226C090ABE6D80D5A96B99E4" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_OtherReceivablesMember" xlink:label="loc_mmsi_OtherReceivablesMember_7EE9A0C84C41204EA04980C0276A4E43" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_383A297A17EBAC97454780C02769F426" xlink:to="loc_mmsi_OtherReceivablesMember_7EE9A0C84C41204EA04980C0276A4E43" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_FC022A29A8C9F9DBB8C880C0276A1EBC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_DC217AE30D3FF3765EA580C0276A4774" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_FC022A29A8C9F9DBB8C880C0276A1EBC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_9A21EBE0071B730CBFA480C0276AD385" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_DC217AE30D3FF3765EA580C0276A4774" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_9A21EBE0071B730CBFA480C0276AD385" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/DerivativesForwardNotionalContractsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeLineItems" xlink:label="loc_us-gaap_DerivativeLineItems_DBF93870AD44E7599A3980C0276E8F3D" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeTable" xlink:label="loc_us-gaap_DerivativeTable_F4843567F3AEA45A5C1E80C0276D18B8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_DBF93870AD44E7599A3980C0276E8F3D" xlink:to="loc_us-gaap_DerivativeTable_F4843567F3AEA45A5C1E80C0276D18B8" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_AFE4476727DFC6B9E6D680E0EF73E7C9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_F4843567F3AEA45A5C1E80C0276D18B8" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_AFE4476727DFC6B9E6D680E0EF73E7C9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="loc_us-gaap_HedgingRelationshipDomain_DE98D67A90F5ACE3069D80E0EF8E3071_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_AFE4476727DFC6B9E6D680E0EF73E7C9" xlink:to="loc_us-gaap_HedgingRelationshipDomain_DE98D67A90F5ACE3069D80E0EF8E3071_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="loc_us-gaap_HedgingRelationshipDomain_DE98D67A90F5ACE3069D80E0EF8E3071" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_AFE4476727DFC6B9E6D680E0EF73E7C9" xlink:to="loc_us-gaap_HedgingRelationshipDomain_DE98D67A90F5ACE3069D80E0EF8E3071" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashFlowHedgingMember" xlink:label="loc_us-gaap_CashFlowHedgingMember_5678020FF0187E208CF880E122D1233A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_DE98D67A90F5ACE3069D80E0EF8E3071" xlink:to="loc_us-gaap_CashFlowHedgingMember_5678020FF0187E208CF880E122D1233A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingDesignationAxis" xlink:label="loc_us-gaap_HedgingDesignationAxis_67A0D23B85437E39EAA580DE01574157" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_F4843567F3AEA45A5C1E80C0276D18B8" xlink:to="loc_us-gaap_HedgingDesignationAxis_67A0D23B85437E39EAA580DE01574157" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="loc_us-gaap_HedgingDesignationDomain_48DD08C5841B900EB7FA80DE0158F57F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_67A0D23B85437E39EAA580DE01574157" xlink:to="loc_us-gaap_HedgingDesignationDomain_48DD08C5841B900EB7FA80DE0158F57F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="loc_us-gaap_HedgingDesignationDomain_48DD08C5841B900EB7FA80DE0158F57F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_67A0D23B85437E39EAA580DE01574157" xlink:to="loc_us-gaap_HedgingDesignationDomain_48DD08C5841B900EB7FA80DE0158F57F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DesignatedAsHedgingInstrumentMember" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_2BC4BBCAA5DF53A3E74380E057170F12" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_48DD08C5841B900EB7FA80DE0158F57F" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_2BC4BBCAA5DF53A3E74380E057170F12" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NondesignatedMember" xlink:label="loc_us-gaap_NondesignatedMember_8EC6B4E380173DD24E0280DE5611B461" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_48DD08C5841B900EB7FA80DE0158F57F" xlink:to="loc_us-gaap_NondesignatedMember_8EC6B4E380173DD24E0280DE5611B461" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_079D5D575AE7705B96D180C0276D523B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_F4843567F3AEA45A5C1E80C0276D18B8" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_079D5D575AE7705B96D180C0276D523B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_4E9DB118EF7BC50EC5FC80C0276DC3AF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_079D5D575AE7705B96D180C0276D523B" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_4E9DB118EF7BC50EC5FC80C0276DC3AF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_4E9DB118EF7BC50EC5FC80C0276DC3AF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_079D5D575AE7705B96D180C0276D523B" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_4E9DB118EF7BC50EC5FC80C0276DC3AF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashFlowHedgingMember" xlink:label="loc_us-gaap_CashFlowHedgingMember_01C19813CC34693CDE6880C0276D4169" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_4E9DB118EF7BC50EC5FC80C0276DC3AF" xlink:to="loc_us-gaap_CashFlowHedgingMember_01C19813CC34693CDE6880C0276D4169" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ForeignExchangeForwardMember" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_423D75F23EB0E8467A7580DF3336B4B1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_4E9DB118EF7BC50EC5FC80C0276DC3AF" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_423D75F23EB0E8467A7580DF3336B4B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_DerivativeNotionalAmount" xlink:label="loc_invest_DerivativeNotionalAmount_0C4CF2549FD04F9EA4BD80C0276E1351" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_DBF93870AD44E7599A3980C0276E8F3D" xlink:to="loc_invest_DerivativeNotionalAmount_0C4CF2549FD04F9EA4BD80C0276E1351" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/DerivativesGainLossInConsolidatedStatementsOfIncomeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeLineItems" xlink:label="loc_us-gaap_DerivativeLineItems_263E62EFA8682DBE1D1B80C0275F5914" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeTable" xlink:label="loc_us-gaap_DerivativeTable_52DEC9D5BB912F5829D780C0275EF1CF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_263E62EFA8682DBE1D1B80C0275F5914" xlink:to="loc_us-gaap_DerivativeTable_52DEC9D5BB912F5829D780C0275EF1CF" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingDesignationAxis" xlink:label="loc_us-gaap_HedgingDesignationAxis_1F229CFBF0A6B644768D80C0275ED85F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_52DEC9D5BB912F5829D780C0275EF1CF" xlink:to="loc_us-gaap_HedgingDesignationAxis_1F229CFBF0A6B644768D80C0275ED85F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="loc_us-gaap_HedgingDesignationDomain_F613930F7C83516CB83B80C0275E8293_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_1F229CFBF0A6B644768D80C0275ED85F" xlink:to="loc_us-gaap_HedgingDesignationDomain_F613930F7C83516CB83B80C0275E8293_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="loc_us-gaap_HedgingDesignationDomain_F613930F7C83516CB83B80C0275E8293" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_1F229CFBF0A6B644768D80C0275ED85F" xlink:to="loc_us-gaap_HedgingDesignationDomain_F613930F7C83516CB83B80C0275E8293" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NondesignatedMember" xlink:label="loc_us-gaap_NondesignatedMember_BFA97B94C7E4B916DE1C80C0275EFEE1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_F613930F7C83516CB83B80C0275E8293" xlink:to="loc_us-gaap_NondesignatedMember_BFA97B94C7E4B916DE1C80C0275EFEE1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_5ADEA87695D3C6EA97B980C0275E6613" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_52DEC9D5BB912F5829D780C0275EF1CF" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_5ADEA87695D3C6EA97B980C0275E6613" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_73B3E2855D69DB91C81B80C0275E2422_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_5ADEA87695D3C6EA97B980C0275E6613" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_73B3E2855D69DB91C81B80C0275E2422_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_73B3E2855D69DB91C81B80C0275E2422" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_5ADEA87695D3C6EA97B980C0275E6613" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_73B3E2855D69DB91C81B80C0275E2422" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ForeignExchangeForwardMember" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_4EEE4A109394E946141080D97C276A6A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_73B3E2855D69DB91C81B80C0275E2422" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_4EEE4A109394E946141080D97C276A6A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_3FC49E4E8049CBE3E95480C0275E23AE" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_52DEC9D5BB912F5829D780C0275EF1CF" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_3FC49E4E8049CBE3E95480C0275E23AE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_6BF8A21ED972F070311D80C0275F0536_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_3FC49E4E8049CBE3E95480C0275E23AE" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_6BF8A21ED972F070311D80C0275F0536_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_6BF8A21ED972F070311D80C0275F0536" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_3FC49E4E8049CBE3E95480C0275E23AE" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_6BF8A21ED972F070311D80C0275F0536" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherExpenseMember" xlink:label="loc_us-gaap_OtherExpenseMember_78024DB29EDAC124187D80C0275F6013" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_6BF8A21ED972F070311D80C0275F0536" xlink:to="loc_us-gaap_OtherExpenseMember_78024DB29EDAC124187D80C0275F6013" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeGainLossOnDerivativeNet" xlink:label="loc_us-gaap_DerivativeGainLossOnDerivativeNet_7852D0E039C57E9866DB80C0275FC70E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_263E62EFA8682DBE1D1B80C0275F5914" xlink:to="loc_us-gaap_DerivativeGainLossOnDerivativeNet_7852D0E039C57E9866DB80C0275FC70E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/DerivativesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeLineItems" xlink:label="loc_us-gaap_DerivativeLineItems_9EEADD2C46C3490ED8808173C812E7F1" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeTable" xlink:label="loc_us-gaap_DerivativeTable_F23B798A41A701A990778173C80F1DCA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_9EEADD2C46C3490ED8808173C812E7F1" xlink:to="loc_us-gaap_DerivativeTable_F23B798A41A701A990778173C80F1DCA" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_3F2F841BAC0FD808FCD68173C810956B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_F23B798A41A701A990778173C80F1DCA" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_3F2F841BAC0FD808FCD68173C810956B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_F840DE9DEB001B0B39618173C810226F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_3F2F841BAC0FD808FCD68173C810956B" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_F840DE9DEB001B0B39618173C810226F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_F840DE9DEB001B0B39618173C810226F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_3F2F841BAC0FD808FCD68173C810956B" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_F840DE9DEB001B0B39618173C810226F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SwapMember" xlink:label="loc_us-gaap_SwapMember_BCD875AF55EAD6C3657A8173C8106FC4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_F840DE9DEB001B0B39618173C810226F" xlink:to="loc_us-gaap_SwapMember_BCD875AF55EAD6C3657A8173C8106FC4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_6449E35DFA9395D0CC118173C81175EC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_F23B798A41A701A990778173C80F1DCA" xlink:to="loc_us-gaap_RangeAxis_6449E35DFA9395D0CC118173C81175EC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_D3B540C349D19F45AFB08173C8113EC8_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_6449E35DFA9395D0CC118173C81175EC" xlink:to="loc_us-gaap_RangeMember_D3B540C349D19F45AFB08173C8113EC8_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_D3B540C349D19F45AFB08173C8113EC8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_6449E35DFA9395D0CC118173C81175EC" xlink:to="loc_us-gaap_RangeMember_D3B540C349D19F45AFB08173C8113EC8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_DA995ABE0158F54C7AF88173C811AAD1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_D3B540C349D19F45AFB08173C8113EC8" xlink:to="loc_us-gaap_MaximumMember_DA995ABE0158F54C7AF88173C811AAD1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_588F2D018162D9313E758173C811EC2F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_F23B798A41A701A990778173C80F1DCA" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_588F2D018162D9313E758173C811EC2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_A0743CC53F644B8769318173C811E99D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_588F2D018162D9313E758173C811EC2F" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_A0743CC53F644B8769318173C811E99D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_A0743CC53F644B8769318173C811E99D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_588F2D018162D9313E758173C811EC2F" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_A0743CC53F644B8769318173C811E99D" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_RevenueandCostofSalesMember" xlink:label="loc_mmsi_RevenueandCostofSalesMember_E580D329F826983DA8598173C812F630" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_A0743CC53F644B8769318173C811E99D" xlink:to="loc_mmsi_RevenueandCostofSalesMember_E580D329F826983DA8598173C812F630" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_InterestExpenseMember" xlink:label="loc_us-gaap_InterestExpenseMember_EBCA719B3349E9C406568173C812E145" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_A0743CC53F644B8769318173C811E99D" xlink:to="loc_us-gaap_InterestExpenseMember_EBCA719B3349E9C406568173C812E145" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_DerivativeNotionalAmount" xlink:label="loc_invest_DerivativeNotionalAmount_CB1547DB5969CED9ABC68173C8123FB4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_9EEADD2C46C3490ED8808173C812E7F1" xlink:to="loc_invest_DerivativeNotionalAmount_CB1547DB5969CED9ABC68173C8123FB4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeFixedInterestRate" xlink:label="loc_us-gaap_DerivativeFixedInterestRate_AAF7A073933300A84CDA8173C81224FE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_9EEADD2C46C3490ED8808173C812E7F1" xlink:to="loc_us-gaap_DerivativeFixedInterestRate_AAF7A073933300A84CDA8173C81224FE" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_DerivativeQuarterlyReductionofNotionalAmount" xlink:label="loc_mmsi_DerivativeQuarterlyReductionofNotionalAmount_F345ECEA3B0F1F2A64158173C81261CF" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_9EEADD2C46C3490ED8808173C812E7F1" xlink:to="loc_mmsi_DerivativeQuarterlyReductionofNotionalAmount_F345ECEA3B0F1F2A64158173C81261CF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_4C22063D6037BC56052D8173C81276D5" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_9EEADD2C46C3490ED8808173C812E7F1" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_4C22063D6037BC56052D8173C81276D5" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesTax" xlink:label="loc_mmsi_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesTax_8F0C87CF9722EC7C0B478173C812FBB3" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_9EEADD2C46C3490ED8808173C812E7F1" xlink:to="loc_mmsi_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesTax_8F0C87CF9722EC7C0B478173C812FBB3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_InterestRateCashFlowHedgeAssetAtFairValue" xlink:label="loc_us-gaap_InterestRateCashFlowHedgeAssetAtFairValue_B05DC354E16914BD94D38173C8135B2A" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_9EEADD2C46C3490ED8808173C812E7F1" xlink:to="loc_us-gaap_InterestRateCashFlowHedgeAssetAtFairValue_B05DC354E16914BD94D38173C8135B2A" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonthsGross" xlink:label="loc_mmsi_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonthsGross_0FC0419B04908CA9E6888173C81343D2" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_9EEADD2C46C3490ED8808173C812E7F1" xlink:to="loc_mmsi_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonthsGross_0FC0419B04908CA9E6888173C81343D2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths" xlink:label="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_9627D56849125AEC958E8173C8138A3A" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_9EEADD2C46C3490ED8808173C812E7F1" xlink:to="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_9627D56849125AEC958E8173C8138A3A" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/DerivativesPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/DerivativesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/DocumentAndEntityInformation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/EarningsPerCommonShareEps" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/EarningsPerCommonShareEpsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/EarningsPerCommonShareEpsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/EmployeeBenefitPlans" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/EmployeeBenefitPlansDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DefinedContributionPlanDisclosureLineItems" xlink:label="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_3E54D8BEE9C626DFD3C3D27CC8CF1380" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DefinedContributionPlanTable" xlink:label="loc_us-gaap_DefinedContributionPlanTable_E45FA9174E390EF31915D27CC8C9413E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_3E54D8BEE9C626DFD3C3D27CC8CF1380" xlink:to="loc_us-gaap_DefinedContributionPlanTable_E45FA9174E390EF31915D27CC8C9413E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TitleOfIndividualAxis" xlink:label="loc_us-gaap_TitleOfIndividualAxis_4C6D639FD67F499EAA5ED27CC8C9E813" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedContributionPlanTable_E45FA9174E390EF31915D27CC8C9413E" xlink:to="loc_us-gaap_TitleOfIndividualAxis_4C6D639FD67F499EAA5ED27CC8C9E813" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_D51E2383A12A9A3FE185D27CC8C94922_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TitleOfIndividualAxis_4C6D639FD67F499EAA5ED27CC8C9E813" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_D51E2383A12A9A3FE185D27CC8C94922_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_D51E2383A12A9A3FE185D27CC8C94922" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TitleOfIndividualAxis_4C6D639FD67F499EAA5ED27CC8C9E813" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_D51E2383A12A9A3FE185D27CC8C94922" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ManagementMember" xlink:label="loc_us-gaap_ManagementMember_3FDE09683E2213998B6ED27CC8C98764" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_D51E2383A12A9A3FE185D27CC8C94922" xlink:to="loc_us-gaap_ManagementMember_3FDE09683E2213998B6ED27CC8C98764" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_76FC81946DB06068BE2AD27CC8C99505" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedContributionPlanTable_E45FA9174E390EF31915D27CC8C9413E" xlink:to="loc_us-gaap_RangeAxis_76FC81946DB06068BE2AD27CC8C99505" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_4C7EA4E6FF7796D59D0FD27CC8C9A418_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_76FC81946DB06068BE2AD27CC8C99505" xlink:to="loc_us-gaap_RangeMember_4C7EA4E6FF7796D59D0FD27CC8C9A418_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_4C7EA4E6FF7796D59D0FD27CC8C9A418" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_76FC81946DB06068BE2AD27CC8C99505" xlink:to="loc_us-gaap_RangeMember_4C7EA4E6FF7796D59D0FD27CC8C9A418" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_B5473606B64BFD369B88D27CC8C95EC9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_4C7EA4E6FF7796D59D0FD27CC8C9A418" xlink:to="loc_us-gaap_MinimumMember_B5473606B64BFD369B88D27CC8C95EC9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_A51414C3125FC88C780BD27CC8C9EE02" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_4C7EA4E6FF7796D59D0FD27CC8C9A418" xlink:to="loc_us-gaap_MaximumMember_A51414C3125FC88C780BD27CC8C9EE02" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="loc_us-gaap_StatementGeographicalAxis_F8E8AD24ABED8242A7D0D27CC8C946E2" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedContributionPlanTable_E45FA9174E390EF31915D27CC8C9413E" xlink:to="loc_us-gaap_StatementGeographicalAxis_F8E8AD24ABED8242A7D0D27CC8C946E2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_B0C5AEF95EFF812F7F7FD27CC8CE0E4C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementGeographicalAxis_F8E8AD24ABED8242A7D0D27CC8C946E2" xlink:to="loc_us-gaap_SegmentGeographicalDomain_B0C5AEF95EFF812F7F7FD27CC8CE0E4C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_B0C5AEF95EFF812F7F7FD27CC8CE0E4C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementGeographicalAxis_F8E8AD24ABED8242A7D0D27CC8C946E2" xlink:to="loc_us-gaap_SegmentGeographicalDomain_B0C5AEF95EFF812F7F7FD27CC8CE0E4C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NonUsMember" xlink:label="loc_us-gaap_NonUsMember_4B9655E85EFC30060ACAD27CC8CEC0D9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_B0C5AEF95EFF812F7F7FD27CC8CE0E4C" xlink:to="loc_us-gaap_NonUsMember_4B9655E85EFC30060ACAD27CC8CEC0D9" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_DefinedContributionPlanMinimumAgeRequirement" xlink:label="loc_mmsi_DefinedContributionPlanMinimumAgeRequirement_415484EBEB9AE6FC1094D27CC8CF9444" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_3E54D8BEE9C626DFD3C3D27CC8CF1380" xlink:to="loc_mmsi_DefinedContributionPlanMinimumAgeRequirement_415484EBEB9AE6FC1094D27CC8CF9444" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_DefinedContributionPlanMinimumServiceRequirement" xlink:label="loc_mmsi_DefinedContributionPlanMinimumServiceRequirement_89953CBC95AB85555266D27CC8CF3A37" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_3E54D8BEE9C626DFD3C3D27CC8CF1380" xlink:to="loc_mmsi_DefinedContributionPlanMinimumServiceRequirement_89953CBC95AB85555266D27CC8CF3A37" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DefinedContributionPlanCostRecognized" xlink:label="loc_us-gaap_DefinedContributionPlanCostRecognized_D7B6F148C7BFFEAAF515D27CC8CF7082" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_3E54D8BEE9C626DFD3C3D27CC8CF1380" xlink:to="loc_us-gaap_DefinedContributionPlanCostRecognized_D7B6F148C7BFFEAAF515D27CC8CF7082" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent" xlink:label="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_1BDB279F18F23F6C2743D27CC8CF7D84" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_3E54D8BEE9C626DFD3C3D27CC8CF1380" xlink:to="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_1BDB279F18F23F6C2743D27CC8CF7D84" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrants" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrantsAllocationOfRecognizedPeriodCostsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_FBDAA13A168562B77FD647FDC8DF0081" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_45C7FDD70BDECC37B84A47FDC8DE4BDF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_FBDAA13A168562B77FD647FDC8DF0081" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_45C7FDD70BDECC37B84A47FDC8DE4BDF" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_53194CA432A0A62E40C347FDC8DF9D07" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_45C7FDD70BDECC37B84A47FDC8DE4BDF" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_53194CA432A0A62E40C347FDC8DF9D07" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_271B70753759ACA7B99A47FDC8DFC162_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_53194CA432A0A62E40C347FDC8DF9D07" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_271B70753759ACA7B99A47FDC8DFC162_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_271B70753759ACA7B99A47FDC8DFC162" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_53194CA432A0A62E40C347FDC8DF9D07" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_271B70753759ACA7B99A47FDC8DFC162" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CostOfSalesMember" xlink:label="loc_us-gaap_CostOfSalesMember_D50FD625237E0C410A6747FDC8DFF34B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_271B70753759ACA7B99A47FDC8DFC162" xlink:to="loc_us-gaap_CostOfSalesMember_D50FD625237E0C410A6747FDC8DFF34B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_77B6C64CAB6443FA388947FDC8DF3501" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_271B70753759ACA7B99A47FDC8DFC162" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_77B6C64CAB6443FA388947FDC8DF3501" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_432C2159A337B1F93E7D47FDC8DFD67A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_271B70753759ACA7B99A47FDC8DFC162" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_432C2159A337B1F93E7D47FDC8DFD67A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_B7F1C9A418837C437CC547FDC8DF618B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_FBDAA13A168562B77FD647FDC8DF0081" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_B7F1C9A418837C437CC547FDC8DF618B" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrantsFairValueCalculationAssumptionsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94CE2E4BCD1C445B25B5D27CCBABA550" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_E04C8491CA737B75F200D27CCBAB1579" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94CE2E4BCD1C445B25B5D27CCBABA550" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_E04C8491CA737B75F200D27CCBAB1579" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_2F09A0819CFA25ED4F77D27CCBABA2F8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_E04C8491CA737B75F200D27CCBAB1579" xlink:to="loc_us-gaap_RangeAxis_2F09A0819CFA25ED4F77D27CCBABA2F8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_F1EFD9F9663708027B64D27CCBAB1F2B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_2F09A0819CFA25ED4F77D27CCBABA2F8" xlink:to="loc_us-gaap_RangeMember_F1EFD9F9663708027B64D27CCBAB1F2B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_F1EFD9F9663708027B64D27CCBAB1F2B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_2F09A0819CFA25ED4F77D27CCBABA2F8" xlink:to="loc_us-gaap_RangeMember_F1EFD9F9663708027B64D27CCBAB1F2B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_6F90DC74FF7B401B7721D27CCBAB3EB5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_F1EFD9F9663708027B64D27CCBAB1F2B" xlink:to="loc_us-gaap_MinimumMember_6F90DC74FF7B401B7721D27CCBAB3EB5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_9F5A18793E660197300ED27CCBAB415D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_F1EFD9F9663708027B64D27CCBAB1F2B" xlink:to="loc_us-gaap_MaximumMember_9F5A18793E660197300ED27CCBAB415D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_169511FD6C1AFE47476DD27CCBABC094" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94CE2E4BCD1C445B25B5D27CCBABA550" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_169511FD6C1AFE47476DD27CCBABC094" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_AA323B20BA6617852875D27CCBAB8CF6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94CE2E4BCD1C445B25B5D27CCBABA550" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_AA323B20BA6617852875D27CCBAB8CF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_F8E38A9069972612AA1CD27CCBABD555" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94CE2E4BCD1C445B25B5D27CCBABA550" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_F8E38A9069972612AA1CD27CCBABD555" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_6B899ED342FFEF3CCABED27CCBACC17A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94CE2E4BCD1C445B25B5D27CCBABA550" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_6B899ED342FFEF3CCABED27CCBACC17A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_95F2EF7A8105BD2EA464D27CCBAC0721" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94CE2E4BCD1C445B25B5D27CCBABA550" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_95F2EF7A8105BD2EA464D27CCBAC0721" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_D01BDAFCDAE95F173801D27CCBAC58D4" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94CE2E4BCD1C445B25B5D27CCBABA550" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_D01BDAFCDAE95F173801D27CCBAC58D4" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrantsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_3F36090F6A1DEA11EF8CD27CC8FA19B8" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D54907681C030CB26A4CD27CC8F99D53" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_3F36090F6A1DEA11EF8CD27CC8FA19B8" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D54907681C030CB26A4CD27CC8F99D53" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_CBEC63B6569A568509D4D27CC8F94FEF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D54907681C030CB26A4CD27CC8F99D53" xlink:to="loc_us-gaap_AwardTypeAxis_CBEC63B6569A568509D4D27CC8F94FEF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_FBEDF86F8979590584F5D27CC8F93C10_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_CBEC63B6569A568509D4D27CC8F94FEF" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_FBEDF86F8979590584F5D27CC8F93C10_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_FBEDF86F8979590584F5D27CC8F93C10" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_CBEC63B6569A568509D4D27CC8F94FEF" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_FBEDF86F8979590584F5D27CC8F93C10" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_9D7A9AA8DE5323C07A61D27CC8F9F4BD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_FBEDF86F8979590584F5D27CC8F93C10" xlink:to="loc_us-gaap_EmployeeStockOptionMember_9D7A9AA8DE5323C07A61D27CC8F9F4BD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PerformanceSharesMember" xlink:label="loc_us-gaap_PerformanceSharesMember_44B25910E35E3DEAE3ECD27CC8F9DC4E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_FBEDF86F8979590584F5D27CC8F93C10" xlink:to="loc_us-gaap_PerformanceSharesMember_44B25910E35E3DEAE3ECD27CC8F9DC4E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_884CC6D608F439E0E41BD27CC8F9878C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D54907681C030CB26A4CD27CC8F99D53" xlink:to="loc_us-gaap_RangeAxis_884CC6D608F439E0E41BD27CC8F9878C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_58B9E042727114301044D27CC8F9A53B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_884CC6D608F439E0E41BD27CC8F9878C" xlink:to="loc_us-gaap_RangeMember_58B9E042727114301044D27CC8F9A53B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_58B9E042727114301044D27CC8F9A53B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_884CC6D608F439E0E41BD27CC8F9878C" xlink:to="loc_us-gaap_RangeMember_58B9E042727114301044D27CC8F9A53B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_DD784DE941C7120D2CF8D27CC8FAD3FC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_58B9E042727114301044D27CC8F9A53B" xlink:to="loc_us-gaap_MinimumMember_DD784DE941C7120D2CF8D27CC8FAD3FC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_E0825B2F04E87D241066D27CC8FA9C2E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_58B9E042727114301044D27CC8F9A53B" xlink:to="loc_us-gaap_MaximumMember_E0825B2F04E87D241066D27CC8FA9C2E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_881BC92A5E95A9ACCF04D27CC8FAB200" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D54907681C030CB26A4CD27CC8F99D53" xlink:to="loc_us-gaap_PlanNameAxis_881BC92A5E95A9ACCF04D27CC8FAB200" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_FE14147A5C7DB8A6F905D27CC8FA59B8_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_881BC92A5E95A9ACCF04D27CC8FAB200" xlink:to="loc_us-gaap_PlanNameDomain_FE14147A5C7DB8A6F905D27CC8FA59B8_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_FE14147A5C7DB8A6F905D27CC8FA59B8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_881BC92A5E95A9ACCF04D27CC8FAB200" xlink:to="loc_us-gaap_PlanNameDomain_FE14147A5C7DB8A6F905D27CC8FA59B8" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_LongTermIncentivePlan2006Member" xlink:label="loc_mmsi_LongTermIncentivePlan2006Member_BDB694D0678D539B5875D27CC8FA6253" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_FE14147A5C7DB8A6F905D27CC8FA59B8" xlink:to="loc_mmsi_LongTermIncentivePlan2006Member_BDB694D0678D539B5875D27CC8FA6253" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_EmployeeStockPurchasePlanQualifiedMember" xlink:label="loc_mmsi_EmployeeStockPurchasePlanQualifiedMember_F24086634640280CCABDD27CC8FA229B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_FE14147A5C7DB8A6F905D27CC8FA59B8" xlink:to="loc_mmsi_EmployeeStockPurchasePlanQualifiedMember_F24086634640280CCABDD27CC8FA229B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_A3746065615245707960D27CC8FA1DC7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_3F36090F6A1DEA11EF8CD27CC8FA19B8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_A3746065615245707960D27CC8FA1DC7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_410AA376610A84E8537CD27CC8FAABB9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_3F36090F6A1DEA11EF8CD27CC8FA19B8" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_410AA376610A84E8537CD27CC8FAABB9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_AB24A2F019B2A65817C1D27CC8FA7BD4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_3F36090F6A1DEA11EF8CD27CC8FA19B8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_AB24A2F019B2A65817C1D27CC8FA7BD4" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_ShareBasedCompensationArrangementEmployeeStockPurchasePlanPercentageofMarketPricePurchaseDate" xlink:label="loc_mmsi_ShareBasedCompensationArrangementEmployeeStockPurchasePlanPercentageofMarketPricePurchaseDate_AD54F67F663BF9C574AED27CC8FA2F0E" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_3F36090F6A1DEA11EF8CD27CC8FA19B8" xlink:to="loc_mmsi_ShareBasedCompensationArrangementEmployeeStockPurchasePlanPercentageofMarketPricePurchaseDate_AD54F67F663BF9C574AED27CC8FA2F0E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_D5DE4C39F90E57FB0FB4D27CC8FAAA32" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_3F36090F6A1DEA11EF8CD27CC8FA19B8" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_D5DE4C39F90E57FB0FB4D27CC8FAAA32" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_4C0AB6C3F1ECCD0A9FE1D27CC8FA5F62" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_3F36090F6A1DEA11EF8CD27CC8FA19B8" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_4C0AB6C3F1ECCD0A9FE1D27CC8FA5F62" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_6D2C3C0B0DB007906FCCD27CC8FA2310" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_3F36090F6A1DEA11EF8CD27CC8FA19B8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_6D2C3C0B0DB007906FCCD27CC8FA2310" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_FairValueOfStockOptionOnGrantDateNetOfForfeitures" xlink:label="loc_mmsi_FairValueOfStockOptionOnGrantDateNetOfForfeitures_EC61AB56B27FD947BA89D27CC8FABC13" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_3F36090F6A1DEA11EF8CD27CC8FA19B8" xlink:to="loc_mmsi_FairValueOfStockOptionOnGrantDateNetOfForfeitures_EC61AB56B27FD947BA89D27CC8FABC13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_D6A4DEDF69452FC93ACCD27CC8FB6690" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_3F36090F6A1DEA11EF8CD27CC8FA19B8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_D6A4DEDF69452FC93ACCD27CC8FB6690" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrantsOptionsOutstandingDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_E3408EF17C1004D1F2B38105CA62C019" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_86FFA18396CD46801C2C8105CA60E129" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_E3408EF17C1004D1F2B38105CA62C019" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_86FFA18396CD46801C2C8105CA60E129" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_0D9F91E78A5DD85C23358105CA61D30F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_86FFA18396CD46801C2C8105CA60E129" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_0D9F91E78A5DD85C23358105CA61D30F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_278884CBCE901E28F84E8105CA61A589_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_0D9F91E78A5DD85C23358105CA61D30F" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_278884CBCE901E28F84E8105CA61A589_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_278884CBCE901E28F84E8105CA61A589" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_0D9F91E78A5DD85C23358105CA61D30F" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_278884CBCE901E28F84E8105CA61A589" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_RangeOneMember" xlink:label="loc_mmsi_RangeOneMember_1D996DD32D11E61D26518105CA61A875" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_278884CBCE901E28F84E8105CA61A589" xlink:to="loc_mmsi_RangeOneMember_1D996DD32D11E61D26518105CA61A875" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_RangeTwoMember" xlink:label="loc_mmsi_RangeTwoMember_95CE091CBC97CD6E693D8105CA62A78C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_278884CBCE901E28F84E8105CA61A589" xlink:to="loc_mmsi_RangeTwoMember_95CE091CBC97CD6E693D8105CA62A78C" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_RangeThreeMember" xlink:label="loc_mmsi_RangeThreeMember_DFF489566E9DCEECAE298105CA6259E6" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_278884CBCE901E28F84E8105CA61A589" xlink:to="loc_mmsi_RangeThreeMember_DFF489566E9DCEECAE298105CA6259E6" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_RangeFourMember" xlink:label="loc_mmsi_RangeFourMember_E39923E65A14C98841BB8105CA62D133" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_278884CBCE901E28F84E8105CA61A589" xlink:to="loc_mmsi_RangeFourMember_E39923E65A14C98841BB8105CA62D133" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_3678D89C4995B8D295C48105CA62196B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_E3408EF17C1004D1F2B38105CA62C019" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_3678D89C4995B8D295C48105CA62196B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_126F55CF1926A952A6938105CA62029F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_E3408EF17C1004D1F2B38105CA62C019" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_126F55CF1926A952A6938105CA62029F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_E6088B43F960973DEFAD8105CA62AF15" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_E3408EF17C1004D1F2B38105CA62C019" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_E6088B43F960973DEFAD8105CA62AF15" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_11FC5569E17EB556987D8105CA6270B7" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_E3408EF17C1004D1F2B38105CA62C019" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_11FC5569E17EB556987D8105CA6270B7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1_288D9A38CBFFA95845478105CA63EEF6" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_E3408EF17C1004D1F2B38105CA62C019" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1_288D9A38CBFFA95845478105CA63EEF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions_7B9C10F69608F62847B08105CA63084F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_E3408EF17C1004D1F2B38105CA62C019" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions_7B9C10F69608F62847B08105CA63084F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1_44880789D2B57F9B2AF08105CA6366CF" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_E3408EF17C1004D1F2B38105CA62C019" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1_44880789D2B57F9B2AF08105CA6366CF" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrantsStockOptionActivityDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/EmployeeStockPurchasePlanStockOptionsAndWarrantsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/FairValueMeasurements" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/FairValueMeasurementsFairValueInputsLiabilitiesQuantitativeInformationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsLiabilitiesQuantitativeInformationLineItems" xlink:label="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationLineItems_C8107E2E8103D108DF968729F01E5294" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsLiabilitiesQuantitativeInformationTable" xlink:label="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationTable_A6A28215C9CE0D1107DD8729F01ABE69" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationLineItems_C8107E2E8103D108DF968729F01E5294" xlink:to="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationTable_A6A28215C9CE0D1107DD8729F01ABE69" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ContingentConsiderationByTypeAxis" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis_AA1D19991075C70405648729F01BE350" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationTable_A6A28215C9CE0D1107DD8729F01ABE69" xlink:to="loc_us-gaap_ContingentConsiderationByTypeAxis_AA1D19991075C70405648729F01BE350" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ContingentConsiderationTypeDomain" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_F3338AF928B6A79AC86A8729F01C8DC2_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_AA1D19991075C70405648729F01BE350" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_F3338AF928B6A79AC86A8729F01C8DC2_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ContingentConsiderationTypeDomain" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_F3338AF928B6A79AC86A8729F01C8DC2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_AA1D19991075C70405648729F01BE350" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_F3338AF928B6A79AC86A8729F01C8DC2" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_RevenueBasedPaymentsMember" xlink:label="loc_mmsi_RevenueBasedPaymentsMember_2EEE48E0D42EFBF1427B8729F01CCB77" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_F3338AF928B6A79AC86A8729F01C8DC2" xlink:to="loc_mmsi_RevenueBasedPaymentsMember_2EEE48E0D42EFBF1427B8729F01CCB77" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_OtherPaymentsMember" xlink:label="loc_mmsi_OtherPaymentsMember_486A4A1876DF1F285EF08729F01C71DB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_F3338AF928B6A79AC86A8729F01C8DC2" xlink:to="loc_mmsi_OtherPaymentsMember_486A4A1876DF1F285EF08729F01C71DB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_C0B0C9ABFB77B73A636D8729F01C01DC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationTable_A6A28215C9CE0D1107DD8729F01ABE69" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_C0B0C9ABFB77B73A636D8729F01C01DC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_E5CEE33FD16725F70D2E8729F01C73D7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_C0B0C9ABFB77B73A636D8729F01C01DC" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_E5CEE33FD16725F70D2E8729F01C73D7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_E5CEE33FD16725F70D2E8729F01C73D7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_C0B0C9ABFB77B73A636D8729F01C01DC" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_E5CEE33FD16725F70D2E8729F01C73D7" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_ContingentConsiderationMember" xlink:label="loc_mmsi_ContingentConsiderationMember_DE4E015C59EF5175BE768729F01CDB7B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_E5CEE33FD16725F70D2E8729F01C73D7" xlink:to="loc_mmsi_ContingentConsiderationMember_DE4E015C59EF5175BE768729F01CDB7B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_AF6EB53BA64077ACBFC88729F01C5348" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationTable_A6A28215C9CE0D1107DD8729F01ABE69" xlink:to="loc_us-gaap_RangeAxis_AF6EB53BA64077ACBFC88729F01C5348" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_CF2F354912252158E69D8729F01D63CA_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_AF6EB53BA64077ACBFC88729F01C5348" xlink:to="loc_us-gaap_RangeMember_CF2F354912252158E69D8729F01D63CA_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_CF2F354912252158E69D8729F01D63CA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_AF6EB53BA64077ACBFC88729F01C5348" xlink:to="loc_us-gaap_RangeMember_CF2F354912252158E69D8729F01D63CA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_7D9EB6C75981139C367B8729F01D6A9A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_CF2F354912252158E69D8729F01D63CA" xlink:to="loc_us-gaap_MinimumMember_7D9EB6C75981139C367B8729F01D6A9A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_13CC95A95ACF864DB0848729F01D0DC3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_CF2F354912252158E69D8729F01D63CA" xlink:to="loc_us-gaap_MaximumMember_13CC95A95ACF864DB0848729F01D0DC3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationTechniqueAxis" xlink:label="loc_us-gaap_ValuationTechniqueAxis_B3362676C0CAABD86E708729F01D9102" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationTable_A6A28215C9CE0D1107DD8729F01ABE69" xlink:to="loc_us-gaap_ValuationTechniqueAxis_B3362676C0CAABD86E708729F01D9102" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="loc_us-gaap_ValuationTechniqueDomain_76D258F75D6990AA4E1B8729F01D87C7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_B3362676C0CAABD86E708729F01D9102" xlink:to="loc_us-gaap_ValuationTechniqueDomain_76D258F75D6990AA4E1B8729F01D87C7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="loc_us-gaap_ValuationTechniqueDomain_76D258F75D6990AA4E1B8729F01D87C7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_B3362676C0CAABD86E708729F01D9102" xlink:to="loc_us-gaap_ValuationTechniqueDomain_76D258F75D6990AA4E1B8729F01D87C7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeApproachValuationTechniqueMember" xlink:label="loc_us-gaap_IncomeApproachValuationTechniqueMember_0906C08F17EB06F6202F8729F01D4809" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_76D258F75D6990AA4E1B8729F01D87C7" xlink:to="loc_us-gaap_IncomeApproachValuationTechniqueMember_0906C08F17EB06F6202F8729F01D4809" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_AE559AC4609AD2A3E7098729F01D5E13" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationTable_A6A28215C9CE0D1107DD8729F01ABE69" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_AE559AC4609AD2A3E7098729F01D5E13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0C414A2DA8AB223E2A4D8729F01DC7AA_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_AE559AC4609AD2A3E7098729F01D5E13" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0C414A2DA8AB223E2A4D8729F01DC7AA_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0C414A2DA8AB223E2A4D8729F01DC7AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_AE559AC4609AD2A3E7098729F01D5E13" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0C414A2DA8AB223E2A4D8729F01DC7AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_E4A7D0AD8A17A96E30C08729F01E6210" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0C414A2DA8AB223E2A4D8729F01DC7AA" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_E4A7D0AD8A17A96E30C08729F01E6210" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_0DB167E9E2DFA18166AE8729F01E0232" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationLineItems_C8107E2E8103D108DF968729F01E5294" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_0DB167E9E2DFA18166AE8729F01E0232" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_EA4DED2DD43368EB0C558729F01F972F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationLineItems_C8107E2E8103D108DF968729F01E5294" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_EA4DED2DD43368EB0C558729F01F972F" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_FairValueInputsProbabilityOfMilestonePayment" xlink:label="loc_mmsi_FairValueInputsProbabilityOfMilestonePayment_903F19B26B08CE2A8B7A8729F01FB29A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationLineItems_C8107E2E8103D108DF968729F01E5294" xlink:to="loc_mmsi_FairValueInputsProbabilityOfMilestonePayment_903F19B26B08CE2A8B7A8729F01FB29A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsDiscountRate" xlink:label="loc_us-gaap_FairValueInputsDiscountRate_63735D93A61BC4FAB1258729F01F09C3" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsLiabilitiesQuantitativeInformationLineItems_C8107E2E8103D108DF968729F01E5294" xlink:to="loc_us-gaap_FairValueInputsDiscountRate_63735D93A61BC4FAB1258729F01F09C3" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/FairValueMeasurementsFinancialAssetsAndLiabilitiesCarriedAtFairValueDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_40307E2FA630DB73101187685B7B7661" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_A7B3AA10975445DD15DC87685B79BFE6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_40307E2FA630DB73101187685B7B7661" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_A7B3AA10975445DD15DC87685B79BFE6" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_6495A3ADFB2F7FCD58B287685B79D1CF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_A7B3AA10975445DD15DC87685B79BFE6" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_6495A3ADFB2F7FCD58B287685B79D1CF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_380D1FCA0048FB3E7BDB87685B7972A7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_6495A3ADFB2F7FCD58B287685B79D1CF" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_380D1FCA0048FB3E7BDB87685B7972A7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_14154167D17A7AA4407F87685B79F926" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_6495A3ADFB2F7FCD58B287685B79D1CF" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_14154167D17A7AA4407F87685B79F926" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_380D1FCA0048FB3E7BDB87685B7972A7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_14154167D17A7AA4407F87685B79F926" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_380D1FCA0048FB3E7BDB87685B7972A7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_71F9271AA00C7F111CB487685B7AACB5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_380D1FCA0048FB3E7BDB87685B7972A7" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_71F9271AA00C7F111CB487685B7AACB5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_19C77E6CD4160C367A0587685B7A2447" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_A7B3AA10975445DD15DC87685B79BFE6" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_19C77E6CD4160C367A0587685B7A2447" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_9CAA4248DCE03ED9B8CD87685B7AF542_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_19C77E6CD4160C367A0587685B7A2447" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_9CAA4248DCE03ED9B8CD87685B7AF542_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_9CAA4248DCE03ED9B8CD87685B7AF542" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_19C77E6CD4160C367A0587685B7A2447" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_9CAA4248DCE03ED9B8CD87685B7AF542" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_6C9467D6F72C8198C1AA87685B7A47F4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_9CAA4248DCE03ED9B8CD87685B7AF542" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_6C9467D6F72C8198C1AA87685B7A47F4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_32C0102B4CFFA8CA155687685B7AD9B1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_A7B3AA10975445DD15DC87685B79BFE6" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_32C0102B4CFFA8CA155687685B7AD9B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_012D894DE2DEB652A70487685B7AC5BC_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_32C0102B4CFFA8CA155687685B7AD9B1" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_012D894DE2DEB652A70487685B7AC5BC_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_012D894DE2DEB652A70487685B7AC5BC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_32C0102B4CFFA8CA155687685B7AD9B1" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_012D894DE2DEB652A70487685B7AC5BC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_307F7788BA03F6E8CC3487685B7A4713" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_012D894DE2DEB652A70487685B7AC5BC" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_307F7788BA03F6E8CC3487685B7A4713" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_34EF9098626C9F301FCB87685B7B1097" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_012D894DE2DEB652A70487685B7AC5BC" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_34EF9098626C9F301FCB87685B7B1097" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_B3B8D44EBB2338E6916587685B7BFE7D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_012D894DE2DEB652A70487685B7AC5BC" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_B3B8D44EBB2338E6916587685B7BFE7D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_InterestRateCashFlowHedgeAssetAtFairValue" xlink:label="loc_us-gaap_InterestRateCashFlowHedgeAssetAtFairValue_E9BFB63C8A179F90E92487685B7B66F9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_40307E2FA630DB73101187685B7B7661" xlink:to="loc_us-gaap_InterestRateCashFlowHedgeAssetAtFairValue_E9BFB63C8A179F90E92487685B7B66F9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ForeignCurrencyContractAssetFairValueDisclosure" xlink:label="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_13B5B831710F7D9E9D4A87685B7B7125" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_40307E2FA630DB73101187685B7B7661" xlink:to="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_13B5B831710F7D9E9D4A87685B7B7125" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure" xlink:label="loc_us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure_CE24069C27E8501D4FB887685B7B625B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_40307E2FA630DB73101187685B7B7661" xlink:to="loc_us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure_CE24069C27E8501D4FB887685B7B625B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue" xlink:label="loc_us-gaap_ForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue_733DAA6519A03E5245DA87685B7BAAEC" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_40307E2FA630DB73101187685B7B7661" xlink:to="loc_us-gaap_ForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue_733DAA6519A03E5245DA87685B7BAAEC" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/FairValueMeasurementsLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_37A908F19D834B9C9F0AD27CC91C6CDB" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_6E9671568A1E26EC5503D27CC91B18CC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_37A908F19D834B9C9F0AD27CC91C6CDB" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_6E9671568A1E26EC5503D27CC91B18CC" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_7E46A0D4480B524E2CCED27CC91B6B6D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_6E9671568A1E26EC5503D27CC91B18CC" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_7E46A0D4480B524E2CCED27CC91B6B6D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_7AAF37C064798734EA9ED27CC91BDF19_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_7E46A0D4480B524E2CCED27CC91B6B6D" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_7AAF37C064798734EA9ED27CC91BDF19_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_7AAF37C064798734EA9ED27CC91BDF19" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_7E46A0D4480B524E2CCED27CC91B6B6D" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_7AAF37C064798734EA9ED27CC91BDF19" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_ContingentConsiderationMember" xlink:label="loc_mmsi_ContingentConsiderationMember_6FF547F862697C686965D27CC91BFEB8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_7AAF37C064798734EA9ED27CC91BDF19" xlink:to="loc_mmsi_ContingentConsiderationMember_6FF547F862697C686965D27CC91BFEB8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_9D46F51ABD4D373FCFCFD27CC91C8284" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_37A908F19D834B9C9F0AD27CC91C6CDB" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_9D46F51ABD4D373FCFCFD27CC91C8284" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_96C5689717E203925653D27CC91C67AC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_9D46F51ABD4D373FCFCFD27CC91C8284" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_96C5689717E203925653D27CC91C67AC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases_9E904FA6B7F48A797533D27CC91C3207" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_9D46F51ABD4D373FCFCFD27CC91C8284" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases_9E904FA6B7F48A797533D27CC91C3207" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_4DD994236ED114111411D27CC91CE072" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_9D46F51ABD4D373FCFCFD27CC91C8284" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_4DD994236ED114111411D27CC91CE072" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_05189FC9F7E41D60BE61D27CC91C8395" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_9D46F51ABD4D373FCFCFD27CC91C8284" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_05189FC9F7E41D60BE61D27CC91C8395" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/FairValueMeasurementsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_5181FEAC1BE9086893838726797A40B3" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_499382DA865F58AFCEAE87267977902D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_5181FEAC1BE9086893838726797A40B3" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_499382DA865F58AFCEAE87267977902D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueByAssetClassAxis" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_D1FFBA7826A249377066872679778997" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_499382DA865F58AFCEAE87267977902D" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_D1FFBA7826A249377066872679778997" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_31DBDD50BF4F22DD789387267977E857_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_D1FFBA7826A249377066872679778997" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_31DBDD50BF4F22DD789387267977E857_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_31DBDD50BF4F22DD789387267977E857" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_D1FFBA7826A249377066872679778997" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_31DBDD50BF4F22DD789387267977E857" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_ContingentConsiderationMember" xlink:label="loc_mmsi_ContingentConsiderationMember_9F518B112FABC04DA9BF872679778B1C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_31DBDD50BF4F22DD789387267977E857" xlink:to="loc_mmsi_ContingentConsiderationMember_9F518B112FABC04DA9BF872679778B1C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ContingentConsiderationByTypeAxis" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis_44A916E467D40FB0334287267978A7F7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_499382DA865F58AFCEAE87267977902D" xlink:to="loc_us-gaap_ContingentConsiderationByTypeAxis_44A916E467D40FB0334287267978A7F7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ContingentConsiderationTypeDomain" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_2B75A2B889D6388F514C87267978BC38_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_44A916E467D40FB0334287267978A7F7" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_2B75A2B889D6388F514C87267978BC38_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ContingentConsiderationTypeDomain" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_2B75A2B889D6388F514C87267978BC38" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_44A916E467D40FB0334287267978A7F7" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_2B75A2B889D6388F514C87267978BC38" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_OtherPaymentsMember" xlink:label="loc_mmsi_OtherPaymentsMember_8134259706007A02FBA7872679783667" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_2B75A2B889D6388F514C87267978BC38" xlink:to="loc_mmsi_OtherPaymentsMember_8134259706007A02FBA7872679783667" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_ContingentReceivableMember" xlink:label="loc_mmsi_ContingentReceivableMember_ACBD7ACD430721AD9023872679786AAB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_2B75A2B889D6388F514C87267978BC38" xlink:to="loc_mmsi_ContingentReceivableMember_ACBD7ACD430721AD9023872679786AAB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_60266F9A90B59E11841787267978B69F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_499382DA865F58AFCEAE87267977902D" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_60266F9A90B59E11841787267978B69F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_7571388D35F465EDE03087267978E63E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_60266F9A90B59E11841787267978B69F" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_7571388D35F465EDE03087267978E63E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_7571388D35F465EDE03087267978E63E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_60266F9A90B59E11841787267978B69F" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_7571388D35F465EDE03087267978E63E" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_ContingentConsiderationMember" xlink:label="loc_mmsi_ContingentConsiderationMember_DF8624175B9555FA1D808726797985A7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_7571388D35F465EDE03087267978E63E" xlink:to="loc_mmsi_ContingentConsiderationMember_DF8624175B9555FA1D808726797985A7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_7AB9C1BD5F2FD889F2528726797A6CA8" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_499382DA865F58AFCEAE87267977902D" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_7AB9C1BD5F2FD889F2528726797A6CA8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_D65D6FA0A8B4A7BFC8A68726797AD315_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_7AB9C1BD5F2FD889F2528726797A6CA8" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_D65D6FA0A8B4A7BFC8A68726797AD315_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_D65D6FA0A8B4A7BFC8A68726797AD315" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_7AB9C1BD5F2FD889F2528726797A6CA8" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_D65D6FA0A8B4A7BFC8A68726797AD315" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_OtherLongTermObligationsMember" xlink:label="loc_mmsi_OtherLongTermObligationsMember_E4228C6A5C447D8690E58726797AB382" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_D65D6FA0A8B4A7BFC8A68726797AD315" xlink:to="loc_mmsi_OtherLongTermObligationsMember_E4228C6A5C447D8690E58726797AB382" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccruedLiabilitiesMember" xlink:label="loc_us-gaap_AccruedLiabilitiesMember_E2A615C09C9958C78AC18726797AFD85" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_D65D6FA0A8B4A7BFC8A68726797AD315" xlink:to="loc_us-gaap_AccruedLiabilitiesMember_E2A615C09C9958C78AC18726797AFD85" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherNoncurrentAssetsMember" xlink:label="loc_us-gaap_OtherNoncurrentAssetsMember_31C4901B26BA20C422E78726797AE6B0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_D65D6FA0A8B4A7BFC8A68726797AD315" xlink:to="loc_us-gaap_OtherNoncurrentAssetsMember_31C4901B26BA20C422E78726797AE6B0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherCurrentAssetsMember" xlink:label="loc_us-gaap_OtherCurrentAssetsMember_6383FB4DD250ACFAA5A68726797A116C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_D65D6FA0A8B4A7BFC8A68726797AD315" xlink:to="loc_us-gaap_OtherCurrentAssetsMember_6383FB4DD250ACFAA5A68726797A116C" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedContingentLiabilityNoncurrent" xlink:label="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedContingentLiabilityNoncurrent_8F3804CAC4FA86443D8E8726797A9111" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_5181FEAC1BE9086893838726797A40B3" xlink:to="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedContingentLiabilityNoncurrent_8F3804CAC4FA86443D8E8726797A9111" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedContingentLiabilityCurrent" xlink:label="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedContingentLiabilityCurrent_971B4636077712AF7E358726797B9517" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_5181FEAC1BE9086893838726797A40B3" xlink:to="loc_mmsi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedContingentLiabilityCurrent_971B4636077712AF7E358726797B9517" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherAssetImpairmentCharges" xlink:label="loc_us-gaap_OtherAssetImpairmentCharges_12B1C0C7762831ECE6DD8726797B018D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_5181FEAC1BE9086893838726797A40B3" xlink:to="loc_us-gaap_OtherAssetImpairmentCharges_12B1C0C7762831ECE6DD8726797B018D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_1072CDAFCF03055F1BAB8726797B9195" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_5181FEAC1BE9086893838726797A40B3" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_1072CDAFCF03055F1BAB8726797B9195" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_B4BECBE7ADC0345E15278726797B3E77" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_5181FEAC1BE9086893838726797A40B3" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_B4BECBE7ADC0345E15278726797B3E77" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_FFD239C88F2A309A1A398726797BB9B8" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_5181FEAC1BE9086893838726797A40B3" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_FFD239C88F2A309A1A398726797BB9B8" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/FairValueMeasurementsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/GoodwillAndIntangibleAssets" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/GoodwillAndIntangibleAssetsFutureAmortizationExpenseDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/GoodwillAndIntangibleAssetsGoodwillDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/GoodwillAndIntangibleAssetsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_03122F50A68438D6DB378114F86191BE" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_85CACC1B26ECA99C62378114F86164F8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_03122F50A68438D6DB378114F86191BE" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_85CACC1B26ECA99C62378114F86164F8" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_BC2DC2E18D2A92E784B78114F8612A02" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_85CACC1B26ECA99C62378114F86164F8" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_BC2DC2E18D2A92E784B78114F8612A02" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_D2663963AAD47A9694C28114F8613364_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_BC2DC2E18D2A92E784B78114F8612A02" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_D2663963AAD47A9694C28114F8613364_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_D2663963AAD47A9694C28114F8613364" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_BC2DC2E18D2A92E784B78114F8612A02" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_D2663963AAD47A9694C28114F8613364" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_OstialSolutionsLlcMember" xlink:label="loc_mmsi_OstialSolutionsLlcMember_19955CDADD2490ACBEB98114F86142A7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_D2663963AAD47A9694C28114F8613364" xlink:to="loc_mmsi_OstialSolutionsLlcMember_19955CDADD2490ACBEB98114F86142A7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillImpairedAccumulatedImpairmentLoss" xlink:label="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_F9C1B00898820BF608318114F861019E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_03122F50A68438D6DB378114F86191BE" xlink:to="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_F9C1B00898820BF608318114F861019E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_7A5BE21EBB9F404767138114F8619CF4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_03122F50A68438D6DB378114F86191BE" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_7A5BE21EBB9F404767138114F8619CF4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillAndIntangibleAssetImpairment" xlink:label="loc_us-gaap_GoodwillAndIntangibleAssetImpairment_6D89CCF00272F4D8209B8114F861F379" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_03122F50A68438D6DB378114F86191BE" xlink:to="loc_us-gaap_GoodwillAndIntangibleAssetImpairment_6D89CCF00272F4D8209B8114F861F379" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_2BF5F905670EEDD1C2A38114F8617CE0" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_03122F50A68438D6DB378114F86191BE" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_2BF5F905670EEDD1C2A38114F8617CE0" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/GoodwillAndIntangibleAssetsOtherIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_004F30AE803B2B40C2B6D27CC9BF3AB2" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_1934B846D16264A69312D27CC9BECFC5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_004F30AE803B2B40C2B6D27CC9BF3AB2" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_1934B846D16264A69312D27CC9BECFC5" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_5C44622223FCE1CECB05D27CC9BE3545" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_1934B846D16264A69312D27CC9BECFC5" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_5C44622223FCE1CECB05D27CC9BE3545" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_F052F952CA2064AD7216D27CC9BE2716_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_5C44622223FCE1CECB05D27CC9BE3545" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_F052F952CA2064AD7216D27CC9BE2716_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_F052F952CA2064AD7216D27CC9BE2716" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_5C44622223FCE1CECB05D27CC9BE3545" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_F052F952CA2064AD7216D27CC9BE2716" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_BDCC066C1F7977485296D27CC9BE6AA2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_F052F952CA2064AD7216D27CC9BE2716" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_BDCC066C1F7977485296D27CC9BE6AA2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PatentsMember" xlink:label="loc_us-gaap_PatentsMember_BDB63D65E37513125ABAD27CC9BE9645" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_BDCC066C1F7977485296D27CC9BE6AA2" xlink:to="loc_us-gaap_PatentsMember_BDB63D65E37513125ABAD27CC9BE9645" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DistributionRightsMember" xlink:label="loc_us-gaap_DistributionRightsMember_30AA2FD72C95C3384BCED27CC9BED435" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_BDCC066C1F7977485296D27CC9BE6AA2" xlink:to="loc_us-gaap_DistributionRightsMember_30AA2FD72C95C3384BCED27CC9BED435" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LicensingAgreementsMember" xlink:label="loc_us-gaap_LicensingAgreementsMember_86DA370BE6256DA6F4D3D27CC9BE4DD0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_BDCC066C1F7977485296D27CC9BE6AA2" xlink:to="loc_us-gaap_LicensingAgreementsMember_86DA370BE6256DA6F4D3D27CC9BE4DD0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TrademarksMember" xlink:label="loc_us-gaap_TrademarksMember_7BA08DCC050413D2A267D27CC9BE0A0D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_BDCC066C1F7977485296D27CC9BE6AA2" xlink:to="loc_us-gaap_TrademarksMember_7BA08DCC050413D2A267D27CC9BE0A0D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NoncompeteAgreementsMember" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_5F119C387123DDFDB10FD27CC9BEBDE5" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_BDCC066C1F7977485296D27CC9BE6AA2" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_5F119C387123DDFDB10FD27CC9BEBDE5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CustomerListsMember" xlink:label="loc_us-gaap_CustomerListsMember_06B9A75CB3A9E70C351BD27CC9BEF2A4" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_BDCC066C1F7977485296D27CC9BE6AA2" xlink:to="loc_us-gaap_CustomerListsMember_06B9A75CB3A9E70C351BD27CC9BEF2A4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RoyaltyAgreementsMember" xlink:label="loc_us-gaap_RoyaltyAgreementsMember_4CAC258D023B54A34870D27CC9BF839F" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherIntangibleAssetsMember_BDCC066C1F7977485296D27CC9BE6AA2" xlink:to="loc_us-gaap_RoyaltyAgreementsMember_4CAC258D023B54A34870D27CC9BF839F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_304A5C52B1EC5721A0E2D27CC9BFE6C2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_004F30AE803B2B40C2B6D27CC9BF3AB2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_304A5C52B1EC5721A0E2D27CC9BFE6C2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_3735259AF07E6192FEF8D27CC9BF002B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_004F30AE803B2B40C2B6D27CC9BF3AB2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_3735259AF07E6192FEF8D27CC9BF002B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_7F9D01BEA4F6F2EAD8EDD27CC9BF8DF0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_004F30AE803B2B40C2B6D27CC9BF3AB2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_7F9D01BEA4F6F2EAD8EDD27CC9BF8DF0" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/GoodwillAndIntangibleAssetsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/IncomeTaxes" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/IncomeTaxesComponentsOfIncomeTaxExpenseBenefitDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/IncomeTaxesDeferredTaxAssetsAndLiabilitiesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/IncomeTaxesDomesticAndForeignDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/IncomeTaxesEffectiveIncomeTaxRateReconciliationDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems" xlink:label="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleTable" xlink:label="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleTable_224F946038FA8DD62524D27CC9861A74" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleTable_224F946038FA8DD62524D27CC9861A74" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_CFA5A66F5901856B2A77D27CC987529C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleTable_224F946038FA8DD62524D27CC9861A74" xlink:to="loc_us-gaap_RangeAxis_CFA5A66F5901856B2A77D27CC987529C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_B9D3DF7028644D670B29D27CC98CB313_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_CFA5A66F5901856B2A77D27CC987529C" xlink:to="loc_us-gaap_RangeMember_B9D3DF7028644D670B29D27CC98CB313_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_B9D3DF7028644D670B29D27CC98CB313" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_CFA5A66F5901856B2A77D27CC987529C" xlink:to="loc_us-gaap_RangeMember_B9D3DF7028644D670B29D27CC98CB313" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_07259DCE27006DA12F9BD27CC98C128B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_B9D3DF7028644D670B29D27CC98CB313" xlink:to="loc_us-gaap_MaximumMember_07259DCE27006DA12F9BD27CC98C128B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_BC0603CDF930683DBEEAD27CC98CC129" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_BC0603CDF930683DBEEAD27CC98CC129" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount" xlink:label="loc_us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_C7B037C9B10185E263D4D27CC98C5C3A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_C7B037C9B10185E263D4D27CC98C5C3A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic_DD6E9DA7B2E8AC7E637CD27CC98C73F6" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic_DD6E9DA7B2E8AC7E637CD27CC98C73F6" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_NetOperatingLossCarryforwardsUtilization" xlink:label="loc_mmsi_NetOperatingLossCarryforwardsUtilization_C1FA977B5372FAFA216BD27CC98CDF0C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_mmsi_NetOperatingLossCarryforwardsUtilization_C1FA977B5372FAFA216BD27CC98CDF0C" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_NetOperatingLossCarryforwardsUsedInCurrentPeriod" xlink:label="loc_mmsi_NetOperatingLossCarryforwardsUsedInCurrentPeriod_F08630CE64040F69D926D27CC98C7F1B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_mmsi_NetOperatingLossCarryforwardsUsedInCurrentPeriod_F08630CE64040F69D926D27CC98C7F1B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsForeign" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsForeign_74DDF159B8F624E5528AD27CC98C4F39" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsForeign_74DDF159B8F624E5528AD27CC98C4F39" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_UnrecognizedTaxBenefitsGrossIncludingInterestAndPenalties" xlink:label="loc_mmsi_UnrecognizedTaxBenefitsGrossIncludingInterestAndPenalties_B2F9D03C08DAD1E34527D27CC98C6CCA" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_mmsi_UnrecognizedTaxBenefitsGrossIncludingInterestAndPenalties_B2F9D03C08DAD1E34527D27CC98C6CCA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_2BA9A3147338592A6F35D27CC98D6656" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_2BA9A3147338592A6F35D27CC98D6656" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_DeferredTaxAssetReductioninValuationAllowanceNoncurrent" xlink:label="loc_mmsi_DeferredTaxAssetReductioninValuationAllowanceNoncurrent_0E6AD352B8736697A765D27CC98D3F13" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_mmsi_DeferredTaxAssetReductioninValuationAllowanceNoncurrent_0E6AD352B8736697A765D27CC98D3F13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued_3A572D014A0097D0A14FD27CC98D79BF" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued_3A572D014A0097D0A14FD27CC98D79BF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_32523C49A82AC1E91934D27CC98D5AED" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_32523C49A82AC1E91934D27CC98D5AED" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible" xlink:label="loc_us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible_C1A50D4096FB604D3E0DD27CC98DA97D" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleLineItems_2813BB7A031B5E24CB58D27CC98CCAA5" xlink:to="loc_us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible_C1A50D4096FB604D3E0DD27CC98DA97D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/IncomeTaxesSummaryOfIncomeTaxContingenciesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/IncomeTaxesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/Inventories" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/InventoriesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/InventoriesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesConcentrationOfCreditRiskDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductInformationLineItems" xlink:label="loc_us-gaap_ProductInformationLineItems_6826D99A6770476CBB4F8137D31DEDB1" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfProductInformationTable" xlink:label="loc_us-gaap_ScheduleOfProductInformationTable_5A01FCD7489B8BD02FE88137D30EEE3B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ProductInformationLineItems_6826D99A6770476CBB4F8137D31DEDB1" xlink:to="loc_us-gaap_ScheduleOfProductInformationTable_5A01FCD7489B8BD02FE88137D30EEE3B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_C801F98F36C2D29440F781384595E558" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfProductInformationTable_5A01FCD7489B8BD02FE88137D30EEE3B" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_C801F98F36C2D29440F781384595E558" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_1FA30FB761B61B877B46813AE1C106DE_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_C801F98F36C2D29440F781384595E558" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_1FA30FB761B61B877B46813AE1C106DE_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_1FA30FB761B61B877B46813AE1C106DE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_C801F98F36C2D29440F781384595E558" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_1FA30FB761B61B877B46813AE1C106DE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_87EB5ABD4D431C159C0A8139984AEC26" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_1FA30FB761B61B877B46813AE1C106DE" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_87EB5ABD4D431C159C0A8139984AEC26" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_D143A7D16B41DB7478738138016CCE13" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfProductInformationTable_5A01FCD7489B8BD02FE88137D30EEE3B" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_D143A7D16B41DB7478738138016CCE13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_FB9EF45F77BEC0E32072813B4B4D22D0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_D143A7D16B41DB7478738138016CCE13" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_FB9EF45F77BEC0E32072813B4B4D22D0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_FB9EF45F77BEC0E32072813B4B4D22D0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_D143A7D16B41DB7478738138016CCE13" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_FB9EF45F77BEC0E32072813B4B4D22D0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SalesRevenueNetMember" xlink:label="loc_us-gaap_SalesRevenueNetMember_8461711F65F347256B67813935EA3A27" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_FB9EF45F77BEC0E32072813B4B4D22D0" xlink:to="loc_us-gaap_SalesRevenueNetMember_8461711F65F347256B67813935EA3A27" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskPercentage1" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_B5F87E34335769952A98811EA39398AF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductInformationLineItems_6826D99A6770476CBB4F8137D31DEDB1" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_B5F87E34335769952A98811EA39398AF" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesDeferredCompensationDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_96A510CD07508E0061B3D27CCAEFECEE" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_E499E8F528BEA6C32977D27CCAEE9FBF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_96A510CD07508E0061B3D27CCAEFECEE" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_E499E8F528BEA6C32977D27CCAEE9FBF" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_99D2ABA13CF9CEF86273D27CCAEE2763" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_E499E8F528BEA6C32977D27CCAEE9FBF" xlink:to="loc_us-gaap_RangeAxis_99D2ABA13CF9CEF86273D27CCAEE2763" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_B12949C5B8FEDF282E78D27CCAEE1A7E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_99D2ABA13CF9CEF86273D27CCAEE2763" xlink:to="loc_us-gaap_RangeMember_B12949C5B8FEDF282E78D27CCAEE1A7E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_B12949C5B8FEDF282E78D27CCAEE1A7E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_99D2ABA13CF9CEF86273D27CCAEE2763" xlink:to="loc_us-gaap_RangeMember_B12949C5B8FEDF282E78D27CCAEE1A7E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_461981E37A515E1369B9D27CCAEF800F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_B12949C5B8FEDF282E78D27CCAEE1A7E" xlink:to="loc_us-gaap_MinimumMember_461981E37A515E1369B9D27CCAEF800F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_72AB7C6BAE902698B678D27CCAEF6A49" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_B12949C5B8FEDF282E78D27CCAEE1A7E" xlink:to="loc_us-gaap_MaximumMember_72AB7C6BAE902698B678D27CCAEF6A49" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_883AA9B1D16AD641AA3CD27CCAEFE0B2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_E499E8F528BEA6C32977D27CCAEE9FBF" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_883AA9B1D16AD641AA3CD27CCAEFE0B2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73A0C07D3E55A0B5D643D27CCAEF8715_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_883AA9B1D16AD641AA3CD27CCAEFE0B2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73A0C07D3E55A0B5D643D27CCAEF8715_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73A0C07D3E55A0B5D643D27CCAEF8715" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_883AA9B1D16AD641AA3CD27CCAEFE0B2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73A0C07D3E55A0B5D643D27CCAEF8715" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CustomerListsMember" xlink:label="loc_us-gaap_CustomerListsMember_7B1F9545DF11A627F20ED27CCAEFB2F4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73A0C07D3E55A0B5D643D27CCAEF8715" xlink:to="loc_us-gaap_CustomerListsMember_7B1F9545DF11A627F20ED27CCAEFB2F4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_518F734ED6083C8ED760D27CCAEF58E9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73A0C07D3E55A0B5D643D27CCAEF8715" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_518F734ED6083C8ED760D27CCAEF58E9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DistributionRightsMember" xlink:label="loc_us-gaap_DistributionRightsMember_FC9674F5D291983B8530D27CCAEF195C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73A0C07D3E55A0B5D643D27CCAEF8715" xlink:to="loc_us-gaap_DistributionRightsMember_FC9674F5D291983B8530D27CCAEF195C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LicensingAgreementsMember" xlink:label="loc_us-gaap_LicensingAgreementsMember_5D9E82AE67FD6F1F3D88D27CCAEF29BE" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73A0C07D3E55A0B5D643D27CCAEF8715" xlink:to="loc_us-gaap_LicensingAgreementsMember_5D9E82AE67FD6F1F3D88D27CCAEF29BE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NoncompeteAgreementsMember" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_885B4FCD7B9617CB2FA4D27CCAEF2A16" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73A0C07D3E55A0B5D643D27CCAEF8715" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_885B4FCD7B9617CB2FA4D27CCAEF2A16" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PatentsMember" xlink:label="loc_us-gaap_PatentsMember_FA88FFEEDCB6B1F81FDCD27CCAEF22BE" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73A0C07D3E55A0B5D643D27CCAEF8715" xlink:to="loc_us-gaap_PatentsMember_FA88FFEEDCB6B1F81FDCD27CCAEF22BE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RoyaltyAgreementsMember" xlink:label="loc_us-gaap_RoyaltyAgreementsMember_D111382F057FBB382751D27CCAEF0C47" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73A0C07D3E55A0B5D643D27CCAEF8715" xlink:to="loc_us-gaap_RoyaltyAgreementsMember_D111382F057FBB382751D27CCAEF0C47" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_A11D1B63B07B43B7721FD27CCAEF6D6E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_96A510CD07508E0061B3D27CCAEFECEE" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_A11D1B63B07B43B7721FD27CCAEF6D6E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesOrganizationDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesOtherAssetsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesPropertyAndEquipmentDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_9AF3FDC5F3D4F12AA47A8114F8A4CC3E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_834783F69D94D6017E358114F8A01230" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_9AF3FDC5F3D4F12AA47A8114F8A4CC3E" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_834783F69D94D6017E358114F8A01230" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_C6456F3D5F5F8222368D8114F8A1B764" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_834783F69D94D6017E358114F8A01230" xlink:to="loc_us-gaap_RangeAxis_C6456F3D5F5F8222368D8114F8A1B764" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_EE6CDBE4966A3D2847F88114F8A19E04_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_C6456F3D5F5F8222368D8114F8A1B764" xlink:to="loc_us-gaap_RangeMember_EE6CDBE4966A3D2847F88114F8A19E04_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_EE6CDBE4966A3D2847F88114F8A19E04" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_C6456F3D5F5F8222368D8114F8A1B764" xlink:to="loc_us-gaap_RangeMember_EE6CDBE4966A3D2847F88114F8A19E04" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_3D108EA66FA162C676918114F8A202DF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_EE6CDBE4966A3D2847F88114F8A19E04" xlink:to="loc_us-gaap_MinimumMember_3D108EA66FA162C676918114F8A202DF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_99EFDD6A7009E2D460F58114F8A25C51" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_EE6CDBE4966A3D2847F88114F8A19E04" xlink:to="loc_us-gaap_MaximumMember_99EFDD6A7009E2D460F58114F8A25C51" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_D86EBC26C0173A880C978114F8A246A3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_834783F69D94D6017E358114F8A01230" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_D86EBC26C0173A880C978114F8A246A3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_48D60F34951FD35E752B8114F8A39C79_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_D86EBC26C0173A880C978114F8A246A3" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_48D60F34951FD35E752B8114F8A39C79_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_48D60F34951FD35E752B8114F8A39C79" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_D86EBC26C0173A880C978114F8A246A3" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_48D60F34951FD35E752B8114F8A39C79" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BuildingMember" xlink:label="loc_us-gaap_BuildingMember_666E6FD03EAA27EF5FC78114F8A341C0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_48D60F34951FD35E752B8114F8A39C79" xlink:to="loc_us-gaap_BuildingMember_666E6FD03EAA27EF5FC78114F8A341C0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquipmentMember" xlink:label="loc_us-gaap_EquipmentMember_A94E8133364836CDBCF08114F8A46C42" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_48D60F34951FD35E752B8114F8A39C79" xlink:to="loc_us-gaap_EquipmentMember_A94E8133364836CDBCF08114F8A46C42" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_251E272F7423BC04A9628114F8A4A8A9" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_48D60F34951FD35E752B8114F8A39C79" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_251E272F7423BC04A9628114F8A4A8A9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LandImprovementsMember" xlink:label="loc_us-gaap_LandImprovementsMember_29A94108CD850B4237388114F8A4F829" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_48D60F34951FD35E752B8114F8A39C79" xlink:to="loc_us-gaap_LandImprovementsMember_29A94108CD850B4237388114F8A4F829" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LeaseholdImprovementsMember" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_1CCFD2C8C28DE4D819608114F8A43AD7" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_48D60F34951FD35E752B8114F8A39C79" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_1CCFD2C8C28DE4D819608114F8A43AD7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_130C64C254B9952214468114F8A415CE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_9AF3FDC5F3D4F12AA47A8114F8A4CC3E" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_130C64C254B9952214468114F8A415CE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Depreciation" xlink:label="loc_us-gaap_Depreciation_0E43A34C835E9BB47E618114F8A442CE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_9AF3FDC5F3D4F12AA47A8114F8A4CC3E" xlink:to="loc_us-gaap_Depreciation_0E43A34C835E9BB47E618114F8A442CE" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesStockBasedCompensationDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/OrganizationAndSummaryOfSignificantAccountingPoliciesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/QuarterlyResultsOfOperationsUnaudited" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/QuarterlyResultsOfOperationsUnauditedDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/QuarterlyResultsOfOperationsUnauditedTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/RevolvingCreditFacilityAndLongTermDebt" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/RevolvingCreditFacilityAndLongTermDebtFinancialCovenantsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems_A6B7CF4B5AEE4807F1358105CAFF5B72" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaap_DebtInstrumentTable_EB4EBFE5ACC5C73DFF9C8105CAFEA37D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_A6B7CF4B5AEE4807F1358105CAFF5B72" xlink:to="loc_us-gaap_DebtInstrumentTable_EB4EBFE5ACC5C73DFF9C8105CAFEA37D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_DebtCovenantPeriodAxis" xlink:label="loc_mmsi_DebtCovenantPeriodAxis_8C335628818BA674C89E8105CAFEE256" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_EB4EBFE5ACC5C73DFF9C8105CAFEA37D" xlink:to="loc_mmsi_DebtCovenantPeriodAxis_8C335628818BA674C89E8105CAFEE256" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_DebtCovenantPeriodDomain" xlink:label="loc_mmsi_DebtCovenantPeriodDomain_69D9F6CF3C1DCF093CAB8105CAFE9F43_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_mmsi_DebtCovenantPeriodAxis_8C335628818BA674C89E8105CAFEE256" xlink:to="loc_mmsi_DebtCovenantPeriodDomain_69D9F6CF3C1DCF093CAB8105CAFE9F43_default" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_DebtCovenantPeriodDomain" xlink:label="loc_mmsi_DebtCovenantPeriodDomain_69D9F6CF3C1DCF093CAB8105CAFE9F43" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_mmsi_DebtCovenantPeriodAxis_8C335628818BA674C89E8105CAFEE256" xlink:to="loc_mmsi_DebtCovenantPeriodDomain_69D9F6CF3C1DCF093CAB8105CAFE9F43" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_ThroughMarch312017Member" xlink:label="loc_mmsi_ThroughMarch312017Member_D7A7D4828E46D6B2A1EC8105CAFEDF11" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_DebtCovenantPeriodDomain_69D9F6CF3C1DCF093CAB8105CAFE9F43" xlink:to="loc_mmsi_ThroughMarch312017Member_D7A7D4828E46D6B2A1EC8105CAFEDF11" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_April12017throughJune302017Member" xlink:label="loc_mmsi_April12017throughJune302017Member_E88941A8E07335FBB8C48105CAFED2E6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_DebtCovenantPeriodDomain_69D9F6CF3C1DCF093CAB8105CAFE9F43" xlink:to="loc_mmsi_April12017throughJune302017Member_E88941A8E07335FBB8C48105CAFED2E6" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_July12017throughDecember312017Member" xlink:label="loc_mmsi_July12017throughDecember312017Member_6E182D39A9E753184E438105CAFE055C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_DebtCovenantPeriodDomain_69D9F6CF3C1DCF093CAB8105CAFE9F43" xlink:to="loc_mmsi_July12017throughDecember312017Member_6E182D39A9E753184E438105CAFE055C" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_January12018throughMarch312018Member" xlink:label="loc_mmsi_January12018throughMarch312018Member_72BBD0C177788AAF8C298105CAFF5C97" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_DebtCovenantPeriodDomain_69D9F6CF3C1DCF093CAB8105CAFE9F43" xlink:to="loc_mmsi_January12018throughMarch312018Member_72BBD0C177788AAF8C298105CAFF5C97" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_April12018andthereafterMember" xlink:label="loc_mmsi_April12018andthereafterMember_7766C0219AD71216E53F8105CAFF0318" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_DebtCovenantPeriodDomain_69D9F6CF3C1DCF093CAB8105CAFE9F43" xlink:to="loc_mmsi_April12018andthereafterMember_7766C0219AD71216E53F8105CAFF0318" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_38B667677225B9A1339E8105CAFF645A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_EB4EBFE5ACC5C73DFF9C8105CAFEA37D" xlink:to="loc_us-gaap_DebtInstrumentAxis_38B667677225B9A1339E8105CAFF645A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_FD3386C83A406A92AB578105CAFF5AC6_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_38B667677225B9A1339E8105CAFF645A" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_FD3386C83A406A92AB578105CAFF5AC6_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_FD3386C83A406A92AB578105CAFF5AC6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_38B667677225B9A1339E8105CAFF645A" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_FD3386C83A406A92AB578105CAFF5AC6" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CreditAgreementMember" xlink:label="loc_mmsi_CreditAgreementMember_0B69AF56B05F1E16CB4B8105CAFFC2D9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_FD3386C83A406A92AB578105CAFF5AC6" xlink:to="loc_mmsi_CreditAgreementMember_0B69AF56B05F1E16CB4B8105CAFFC2D9" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_LineofCreditFacilityCovenantTermsConsolidatedTotalLeverageRatioMaximum" xlink:label="loc_mmsi_LineofCreditFacilityCovenantTermsConsolidatedTotalLeverageRatioMaximum_916146D5FFFED9249C4C8105CAFF7458" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_A6B7CF4B5AEE4807F1358105CAFF5B72" xlink:to="loc_mmsi_LineofCreditFacilityCovenantTermsConsolidatedTotalLeverageRatioMaximum_916146D5FFFED9249C4C8105CAFF7458" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_LineofCreditFacilityCovenantTermsConsolidatedEbitdaToFixedChargesRatioMinimum1" xlink:label="loc_mmsi_LineofCreditFacilityCovenantTermsConsolidatedEbitdaToFixedChargesRatioMinimum1_7A4F024DCF600B502F9E8105CB0050D0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_A6B7CF4B5AEE4807F1358105CAFF5B72" xlink:to="loc_mmsi_LineofCreditFacilityCovenantTermsConsolidatedEbitdaToFixedChargesRatioMinimum1_7A4F024DCF600B502F9E8105CB0050D0" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_LineofCreditFacilityCovenantTermsConsolidatedNetIncomeMinimum" xlink:label="loc_mmsi_LineofCreditFacilityCovenantTermsConsolidatedNetIncomeMinimum_BAC0A00224FEA8257D258105CB00ED33" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_A6B7CF4B5AEE4807F1358105CAFF5B72" xlink:to="loc_mmsi_LineofCreditFacilityCovenantTermsConsolidatedNetIncomeMinimum_BAC0A00224FEA8257D258105CB00ED33" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_LineOfCreditFacilityCovenantTermsConsolidatedEbitdaToFixedChargesRatioNumberOfConsecutiveQuarters" xlink:label="loc_mmsi_LineOfCreditFacilityCovenantTermsConsolidatedEbitdaToFixedChargesRatioNumberOfConsecutiveQuarters_580202BCCDE8B3A290838105CB001DD8" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_A6B7CF4B5AEE4807F1358105CAFF5B72" xlink:to="loc_mmsi_LineOfCreditFacilityCovenantTermsConsolidatedEbitdaToFixedChargesRatioNumberOfConsecutiveQuarters_580202BCCDE8B3A290838105CB001DD8" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_LineOfCreditFacilityCovenantTermsFacilityCapitalExpendituresNextTwelveMonthsMaximum" xlink:label="loc_mmsi_LineOfCreditFacilityCovenantTermsFacilityCapitalExpendituresNextTwelveMonthsMaximum_96EC5465BBEA0B1E2AAD8105CB00CFAB" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_A6B7CF4B5AEE4807F1358105CAFF5B72" xlink:to="loc_mmsi_LineOfCreditFacilityCovenantTermsFacilityCapitalExpendituresNextTwelveMonthsMaximum_96EC5465BBEA0B1E2AAD8105CB00CFAB" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/RevolvingCreditFacilityAndLongTermDebtFutureMinimumPaymentsOnLongTermDebtDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/RevolvingCreditFacilityAndLongTermDebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_71BE62A916D9F9E990E58173C85433D8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_71BE62A916D9F9E990E58173C85433D8" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_08794B5B66B65A545C1C8173C855CA49" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_71BE62A916D9F9E990E58173C85433D8" xlink:to="loc_us-gaap_RangeAxis_08794B5B66B65A545C1C8173C855CA49" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_BCA6A6298788284615EF8173C8556179_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_08794B5B66B65A545C1C8173C855CA49" xlink:to="loc_us-gaap_RangeMember_BCA6A6298788284615EF8173C8556179_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_BCA6A6298788284615EF8173C8556179" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_08794B5B66B65A545C1C8173C855CA49" xlink:to="loc_us-gaap_RangeMember_BCA6A6298788284615EF8173C8556179" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_7A6C10E1377A90187B838173C8555563" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_BCA6A6298788284615EF8173C8556179" xlink:to="loc_us-gaap_MinimumMember_7A6C10E1377A90187B838173C8555563" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_1D9D2FF082343B30C49F8173C8566C79" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_BCA6A6298788284615EF8173C8556179" xlink:to="loc_us-gaap_MaximumMember_1D9D2FF082343B30C49F8173C8566C79" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_370DF1F3C5C7CB5A1D178173C856467A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_71BE62A916D9F9E990E58173C85433D8" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_370DF1F3C5C7CB5A1D178173C856467A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_9B078CA2930852FD83D68173C8568AB6_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_370DF1F3C5C7CB5A1D178173C856467A" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_9B078CA2930852FD83D68173C8568AB6_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_9B078CA2930852FD83D68173C8568AB6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_370DF1F3C5C7CB5A1D178173C856467A" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_9B078CA2930852FD83D68173C8568AB6" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_InterestRateSwap1Member" xlink:label="loc_mmsi_InterestRateSwap1Member_C21013CFF51962819C8F8173C85641DE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_9B078CA2930852FD83D68173C8568AB6" xlink:to="loc_mmsi_InterestRateSwap1Member_C21013CFF51962819C8F8173C85641DE" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_InterestRateSwap2Member" xlink:label="loc_mmsi_InterestRateSwap2Member_6173C1A55A3A8983893C8173C856D158" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_9B078CA2930852FD83D68173C8568AB6" xlink:to="loc_mmsi_InterestRateSwap2Member_6173C1A55A3A8983893C8173C856D158" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaap_CreditFacilityAxis_7802F76A564FA4956A968173C8569BF3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_71BE62A916D9F9E990E58173C85433D8" xlink:to="loc_us-gaap_CreditFacilityAxis_7802F76A564FA4956A968173C8569BF3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_03732F01DC05C028611F8173C856A3BB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_7802F76A564FA4956A968173C8569BF3" xlink:to="loc_us-gaap_CreditFacilityDomain_03732F01DC05C028611F8173C856A3BB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_03732F01DC05C028611F8173C856A3BB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_7802F76A564FA4956A968173C8569BF3" xlink:to="loc_us-gaap_CreditFacilityDomain_03732F01DC05C028611F8173C856A3BB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RevolvingCreditFacilityMember" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_008057446D24CFC4725E8173C856B31E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_03732F01DC05C028611F8173C856A3BB" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_008057446D24CFC4725E8173C856B31E" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_TermLoanMember" xlink:label="loc_mmsi_TermLoanMember_48E21895024AE501FCAB8173C857C785" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_03732F01DC05C028611F8173C856A3BB" xlink:to="loc_mmsi_TermLoanMember_48E21895024AE501FCAB8173C857C785" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BridgeLoanMember" xlink:label="loc_us-gaap_BridgeLoanMember_BB6891C38DD2C4BA28998173C8579C83" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_03732F01DC05C028611F8173C856A3BB" xlink:to="loc_us-gaap_BridgeLoanMember_BB6891C38DD2C4BA28998173C8579C83" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="loc_us-gaap_LineOfCreditFacilityAxis_DFDCDB8A8404685EE4348173C8579624" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_71BE62A916D9F9E990E58173C85433D8" xlink:to="loc_us-gaap_LineOfCreditFacilityAxis_DFDCDB8A8404685EE4348173C8579624" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_26475AC13C9EAF6F74318173C857B940_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_DFDCDB8A8404685EE4348173C8579624" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_26475AC13C9EAF6F74318173C857B940_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_26475AC13C9EAF6F74318173C857B940" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_DFDCDB8A8404685EE4348173C8579624" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_26475AC13C9EAF6F74318173C857B940" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateAxis" xlink:label="loc_us-gaap_VariableRateAxis_460054F2B4FFB57FE1798173C857B07C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_71BE62A916D9F9E990E58173C85433D8" xlink:to="loc_us-gaap_VariableRateAxis_460054F2B4FFB57FE1798173C857B07C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_B328C036697C456490358173C8574856_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_460054F2B4FFB57FE1798173C857B07C" xlink:to="loc_us-gaap_VariableRateDomain_B328C036697C456490358173C8574856_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_B328C036697C456490358173C8574856" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_460054F2B4FFB57FE1798173C857B07C" xlink:to="loc_us-gaap_VariableRateDomain_B328C036697C456490358173C8574856" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_VariableRate1Member" xlink:label="loc_mmsi_VariableRate1Member_B597530539116E65F2798173C8585674" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_B328C036697C456490358173C8574856" xlink:to="loc_mmsi_VariableRate1Member_B597530539116E65F2798173C8585674" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_VariableRate2Member" xlink:label="loc_mmsi_VariableRate2Member_F2674D44FFC27510FF5A8173C8580BDB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_B328C036697C456490358173C8574856" xlink:to="loc_mmsi_VariableRate2Member_F2674D44FFC27510FF5A8173C8580BDB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_9E8141784EE28E31170D8173C85899D9" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_71BE62A916D9F9E990E58173C85433D8" xlink:to="loc_us-gaap_DebtInstrumentAxis_9E8141784EE28E31170D8173C85899D9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_23489F286235CAA3B11D8173C8583792_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_9E8141784EE28E31170D8173C85899D9" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_23489F286235CAA3B11D8173C8583792_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_23489F286235CAA3B11D8173C8583792" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_9E8141784EE28E31170D8173C85899D9" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_23489F286235CAA3B11D8173C8583792" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CreditAgreementMember" xlink:label="loc_mmsi_CreditAgreementMember_38F6E35A1D20359EB5998173C8598159" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_23489F286235CAA3B11D8173C8583792" xlink:to="loc_mmsi_CreditAgreementMember_38F6E35A1D20359EB5998173C8598159" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentCarryingAmount" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_C571E8204801B9B39D5B8173C859A21C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_C571E8204801B9B39D5B8173C859A21C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_3693D72580D37825C2E68173C859CB6B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_3693D72580D37825C2E68173C859CB6B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_E866DCCBFD98FA3908AB8173C859FB44" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_E866DCCBFD98FA3908AB8173C859FB44" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_DebtInstrumentDebtDefaultIncreaseinInterestRate" xlink:label="loc_mmsi_DebtInstrumentDebtDefaultIncreaseinInterestRate_99C5B8E3AA9CD79056B48173C85911A2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_mmsi_DebtInstrumentDebtDefaultIncreaseinInterestRate_99C5B8E3AA9CD79056B48173C85911A2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_EA8C87E7F975A03A84D68173C85A2B39" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_EA8C87E7F975A03A84D68173C85A2B39" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_LineOfCreditFacilityCovenantTermsConsolidatedEbitdaToFixedChargesRatioNumberOfConsecutiveQuarters" xlink:label="loc_mmsi_LineOfCreditFacilityCovenantTermsConsolidatedEbitdaToFixedChargesRatioNumberOfConsecutiveQuarters_6B45120D5ED9652F4CD88173C85BE08D" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_mmsi_LineOfCreditFacilityCovenantTermsConsolidatedEbitdaToFixedChargesRatioNumberOfConsecutiveQuarters_6B45120D5ED9652F4CD88173C85BE08D" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_LineOfCreditFacilityCovenantTermsFacilityCapitalExpendituresNextTwelveMonthsMaximum" xlink:label="loc_mmsi_LineOfCreditFacilityCovenantTermsFacilityCapitalExpendituresNextTwelveMonthsMaximum_B3A98743EBF3954460878173C85C123E" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_mmsi_LineOfCreditFacilityCovenantTermsFacilityCapitalExpendituresNextTwelveMonthsMaximum_B3A98743EBF3954460878173C85C123E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_437B0490AFA87D0626908173C85CB649" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_437B0490AFA87D0626908173C85CB649" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtPercentageBearingFixedInterestRate" xlink:label="loc_us-gaap_LongTermDebtPercentageBearingFixedInterestRate_064FE07D5C5D5E08F94A8173C85CF8A5" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_us-gaap_LongTermDebtPercentageBearingFixedInterestRate_064FE07D5C5D5E08F94A8173C85CF8A5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtPercentageBearingFixedInterestAmount" xlink:label="loc_us-gaap_LongtermDebtPercentageBearingFixedInterestAmount_EA90A071407B7C86E3438173C85C308F" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_us-gaap_LongtermDebtPercentageBearingFixedInterestAmount_EA90A071407B7C86E3438173C85C308F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtPercentageBearingVariableInterestRate" xlink:label="loc_us-gaap_LongTermDebtPercentageBearingVariableInterestRate_E765F1402F00E4EB4ABA8173C85C6E70" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_us-gaap_LongTermDebtPercentageBearingVariableInterestRate_E765F1402F00E4EB4ABA8173C85C6E70" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtPercentageBearingVariableInterestAmount" xlink:label="loc_us-gaap_LongtermDebtPercentageBearingVariableInterestAmount_928F3C16691CCAF0CB228173C85C91C0" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_3F599DD4CB86E12B61C48173C8597E7C" xlink:to="loc_us-gaap_LongtermDebtPercentageBearingVariableInterestAmount_928F3C16691CCAF0CB228173C85C91C0" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/RevolvingCreditFacilityAndLongTermDebtPrincipalBalancesUnderLongTermDebtDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_795738D97F5D897A8ED48114F82EABAA" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_DEF8BDA1CCBF1E35EF638114F82E8F6B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_795738D97F5D897A8ED48114F82EABAA" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_DEF8BDA1CCBF1E35EF638114F82E8F6B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaap_CreditFacilityAxis_2E701F3265DE030BCFD48114F82E17B6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_DEF8BDA1CCBF1E35EF638114F82E8F6B" xlink:to="loc_us-gaap_CreditFacilityAxis_2E701F3265DE030BCFD48114F82E17B6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_376CDAB4472A2329CB918114F82E50F2_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_2E701F3265DE030BCFD48114F82E17B6" xlink:to="loc_us-gaap_CreditFacilityDomain_376CDAB4472A2329CB918114F82E50F2_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_376CDAB4472A2329CB918114F82E50F2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_2E701F3265DE030BCFD48114F82E17B6" xlink:to="loc_us-gaap_CreditFacilityDomain_376CDAB4472A2329CB918114F82E50F2" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_TermLoanMember" xlink:label="loc_mmsi_TermLoanMember_F1FA921232E2D8555AF08114F82EADA4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_376CDAB4472A2329CB918114F82E50F2" xlink:to="loc_mmsi_TermLoanMember_F1FA921232E2D8555AF08114F82EADA4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RevolvingCreditFacilityMember" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_9B69BABD58AE9E11F6A08114F82EB8B5" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_376CDAB4472A2329CB918114F82E50F2" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_9B69BABD58AE9E11F6A08114F82EB8B5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebt" xlink:label="loc_us-gaap_LongTermDebt_8F92246ACF0D53C857A88114F82E2E7A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_795738D97F5D897A8ED48114F82EABAA" xlink:to="loc_us-gaap_LongTermDebt_8F92246ACF0D53C857A88114F82E2E7A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredFinanceCostsNet" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_425AF616F8E71F02B4308114F82F3A3D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_795738D97F5D897A8ED48114F82EABAA" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_425AF616F8E71F02B4308114F82F3A3D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="loc_us-gaap_LongTermDebtCurrent_B7F3F6D5115EFDE2E1448114F82FDD5E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_795738D97F5D897A8ED48114F82EABAA" xlink:to="loc_us-gaap_LongTermDebtCurrent_B7F3F6D5115EFDE2E1448114F82FDD5E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_BEDC8A3EB0943FCE41078114F82F24F7" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_795738D97F5D897A8ED48114F82EABAA" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_BEDC8A3EB0943FCE41078114F82F24F7" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/RevolvingCreditFacilityAndLongTermDebtTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/RoyaltyAgreements" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/RoyaltyAgreementsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_RoyaltyAgreementsLineItems" xlink:label="loc_mmsi_RoyaltyAgreementsLineItems_B6C78B142AFBFE4973AFD27CCA64FE7D" xlink:type="locator" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_RoyaltyAgreementsTable" xlink:label="loc_mmsi_RoyaltyAgreementsTable_B816F65084F816170ADDD27CCA6405D5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_mmsi_RoyaltyAgreementsLineItems_B6C78B142AFBFE4973AFD27CCA64FE7D" xlink:to="loc_mmsi_RoyaltyAgreementsTable_B816F65084F816170ADDD27CCA6405D5" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_RoyaltyAgreementsAxis" xlink:label="loc_mmsi_RoyaltyAgreementsAxis_12B481AF1F229AD03F37D27CCA6499C6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_mmsi_RoyaltyAgreementsTable_B816F65084F816170ADDD27CCA6405D5" xlink:to="loc_mmsi_RoyaltyAgreementsAxis_12B481AF1F229AD03F37D27CCA6499C6" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_RoyaltyAgreementsDomain" xlink:label="loc_mmsi_RoyaltyAgreementsDomain_385178B9993285A00E0CD27CCA6428F4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_mmsi_RoyaltyAgreementsAxis_12B481AF1F229AD03F37D27CCA6499C6" xlink:to="loc_mmsi_RoyaltyAgreementsDomain_385178B9993285A00E0CD27CCA6428F4_default" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_RoyaltyAgreementsDomain" xlink:label="loc_mmsi_RoyaltyAgreementsDomain_385178B9993285A00E0CD27CCA6428F4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_mmsi_RoyaltyAgreementsAxis_12B481AF1F229AD03F37D27CCA6499C6" xlink:to="loc_mmsi_RoyaltyAgreementsDomain_385178B9993285A00E0CD27CCA6428F4" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_BiosphereAphpRoyaltyMember" xlink:label="loc_mmsi_BiosphereAphpRoyaltyMember_CB39A8E41FB817084B50D27CCA6465A0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_RoyaltyAgreementsDomain_385178B9993285A00E0CD27CCA6428F4" xlink:to="loc_mmsi_BiosphereAphpRoyaltyMember_CB39A8E41FB817084B50D27CCA6465A0" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CurrentRoyaltyRate" xlink:label="loc_mmsi_CurrentRoyaltyRate_1357BD1C3FC62C2B7B83D27CCA6574E7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_RoyaltyAgreementsLineItems_B6C78B142AFBFE4973AFD27CCA64FE7D" xlink:to="loc_mmsi_CurrentRoyaltyRate_1357BD1C3FC62C2B7B83D27CCA6574E7" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_FutureRoyaltyRate" xlink:label="loc_mmsi_FutureRoyaltyRate_B0335C7D31390D093704D27CCA652F4E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_RoyaltyAgreementsLineItems_B6C78B142AFBFE4973AFD27CCA64FE7D" xlink:to="loc_mmsi_FutureRoyaltyRate_B0335C7D31390D093704D27CCA652F4E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RoyaltyExpense" xlink:label="loc_us-gaap_RoyaltyExpense_78D5B500DCC377A78D03D27CCA65A023" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mmsi_RoyaltyAgreementsLineItems_B6C78B142AFBFE4973AFD27CCA64FE7D" xlink:to="loc_us-gaap_RoyaltyExpense_78D5B500DCC377A78D03D27CCA65A023" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/ScheduleIiValuationAndQualifyingAccounts" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/ScheduleIiValuationAndQualifyingAccountsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationAndQualifyingAccountsDisclosureLineItems" xlink:label="loc_us-gaap_ValuationAndQualifyingAccountsDisclosureLineItems_9A4AB55E1CB6E7A69E768AC2EBDB3D6E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationAndQualifyingAccountsDisclosureTable" xlink:label="loc_us-gaap_ValuationAndQualifyingAccountsDisclosureTable_F7EF2100C29C9EE41D7F8AC2EBD64A9B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ValuationAndQualifyingAccountsDisclosureLineItems_9A4AB55E1CB6E7A69E768AC2EBDB3D6E" xlink:to="loc_us-gaap_ValuationAndQualifyingAccountsDisclosureTable_F7EF2100C29C9EE41D7F8AC2EBD64A9B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationAllowancesAndReservesTypeAxis" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_64AF05BFBFA47728FD748AC2EBD80498" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ValuationAndQualifyingAccountsDisclosureTable_F7EF2100C29C9EE41D7F8AC2EBD64A9B" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_64AF05BFBFA47728FD748AC2EBD80498" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationAllowancesAndReservesDomain" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDomain_AC256EE164515C8561F28AC2EBD804A4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_64AF05BFBFA47728FD748AC2EBD80498" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDomain_AC256EE164515C8561F28AC2EBD804A4_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationAllowancesAndReservesDomain" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDomain_AC256EE164515C8561F28AC2EBD804A4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_64AF05BFBFA47728FD748AC2EBD80498" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDomain_AC256EE164515C8561F28AC2EBD804A4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AllowanceForDoubtfulAccountsMember" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsMember_A005A926E46DADB356BB8AC2EBD86D6C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesDomain_AC256EE164515C8561F28AC2EBD804A4" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsMember_A005A926E46DADB356BB8AC2EBD86D6C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationAllowanceOfDeferredTaxAssetsMember" xlink:label="loc_us-gaap_ValuationAllowanceOfDeferredTaxAssetsMember_87F080D45B4AF7E550568AC2EBDBD154" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesDomain_AC256EE164515C8561F28AC2EBD804A4" xlink:to="loc_us-gaap_ValuationAllowanceOfDeferredTaxAssetsMember_87F080D45B4AF7E550568AC2EBDBD154" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MovementInValuationAllowancesAndReservesRollForward" xlink:label="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_214F3AB393EB7E277E498AC2EBDBA3A3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationAndQualifyingAccountsDisclosureLineItems_9A4AB55E1CB6E7A69E768AC2EBDB3D6E" xlink:to="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_214F3AB393EB7E277E498AC2EBDBA3A3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationAllowancesAndReservesBalance" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesBalance_D1069327471B74AD61D48AC2EBDBA6FC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_214F3AB393EB7E277E498AC2EBDBA3A3" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesBalance_D1069327471B74AD61D48AC2EBDBA6FC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense_56FCBB80F5745700E7948AC2EBDDEC79" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_214F3AB393EB7E277E498AC2EBDBA3A3" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense_56FCBB80F5745700E7948AC2EBDDEC79" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationAllowancesAndReservesDeductions" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDeductions_5115DD2E32FD37FDD0E78AC2EBDDC7F4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_214F3AB393EB7E277E498AC2EBDBA3A3" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDeductions_5115DD2E32FD37FDD0E78AC2EBDDC7F4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ValuationAllowancesAndReservesAdjustments" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesAdjustments_EF7C0F7C060E959A78B18AC741A92EE7" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_214F3AB393EB7E277E498AC2EBDBA3A3" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesAdjustments_EF7C0F7C060E959A78B18AC741A92EE7" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/SegmentReportingAndForeignOperations" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/SegmentReportingAndForeignOperationsAssetsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentReportingAssetReconcilingItemLineItems" xlink:label="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_413E024958D2321A02CF806B4792827C" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable" xlink:label="loc_us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable_86AD072E674D37504669806B47908D73" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_413E024958D2321A02CF806B4792827C" xlink:to="loc_us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable_86AD072E674D37504669806B47908D73" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_4BF04B6B89E0BB28EF69806B4791E4C7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable_86AD072E674D37504669806B47908D73" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_4BF04B6B89E0BB28EF69806B4791E4C7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_B953C75C8DD162C7B607806B4791EA63_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_4BF04B6B89E0BB28EF69806B4791E4C7" xlink:to="loc_us-gaap_SegmentDomain_B953C75C8DD162C7B607806B4791EA63_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_B953C75C8DD162C7B607806B4791EA63" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_4BF04B6B89E0BB28EF69806B4791E4C7" xlink:to="loc_us-gaap_SegmentDomain_B953C75C8DD162C7B607806B4791EA63" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CardiovascularSegmentMember" xlink:label="loc_mmsi_CardiovascularSegmentMember_B0239B4896E7B3432AC3806B47915672" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_B953C75C8DD162C7B607806B4791EA63" xlink:to="loc_mmsi_CardiovascularSegmentMember_B0239B4896E7B3432AC3806B47915672" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_EndoscopySegmentMember" xlink:label="loc_mmsi_EndoscopySegmentMember_0B66D07872260EB282B4806B4791CEB2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_B953C75C8DD162C7B607806B4791EA63" xlink:to="loc_mmsi_EndoscopySegmentMember_0B66D07872260EB282B4806B4791CEB2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_0123EE5EBB124D6BE499806B479294D3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_413E024958D2321A02CF806B4792827C" xlink:to="loc_us-gaap_Assets_0123EE5EBB124D6BE499806B479294D3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DepreciationDepletionAndAmortization" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_CC192593E6FDC95AC973806B4792AD12" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_413E024958D2321A02CF806B4792827C" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_CC192593E6FDC95AC973806B4792AD12" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_0F1AB7F799809D306F40806B47937331" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_413E024958D2321A02CF806B4792827C" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_0F1AB7F799809D306F40806B47937331" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/SegmentReportingAndForeignOperationsLongLivedAssetsByGeographicAreaDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_D2D54C3775342942866ED27CCBFF55CF" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_06075471BE4FE9CF7606D27CCBFEB17C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_D2D54C3775342942866ED27CCBFF55CF" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_06075471BE4FE9CF7606D27CCBFEB17C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="loc_us-gaap_StatementGeographicalAxis_692FB49674A231C1756BD27CCBFEC298" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_06075471BE4FE9CF7606D27CCBFEB17C" xlink:to="loc_us-gaap_StatementGeographicalAxis_692FB49674A231C1756BD27CCBFEC298" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_77A352AA605361FFA904D27CCBFEDB93_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementGeographicalAxis_692FB49674A231C1756BD27CCBFEC298" xlink:to="loc_us-gaap_SegmentGeographicalDomain_77A352AA605361FFA904D27CCBFEDB93_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_77A352AA605361FFA904D27CCBFEDB93" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementGeographicalAxis_692FB49674A231C1756BD27CCBFEC298" xlink:to="loc_us-gaap_SegmentGeographicalDomain_77A352AA605361FFA904D27CCBFEDB93" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd#country_US" xlink:label="loc_country_US_D65B518A40DBEEA8C591D27CCBFE8816" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_77A352AA605361FFA904D27CCBFEDB93" xlink:to="loc_country_US_D65B518A40DBEEA8C591D27CCBFE8816" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd#country_IE" xlink:label="loc_country_IE_4FC98C36BF499517183FD27CCBFF6E05" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_77A352AA605361FFA904D27CCBFEDB93" xlink:to="loc_country_IE_4FC98C36BF499517183FD27CCBFF6E05" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_NonUSExcludingIrelandMember" xlink:label="loc_mmsi_NonUSExcludingIrelandMember_EDED00CDD895B600DDA4D27CCBFF5BE0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_77A352AA605361FFA904D27CCBFEDB93" xlink:to="loc_mmsi_NonUSExcludingIrelandMember_EDED00CDD895B600DDA4D27CCBFF5BE0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NoncurrentAssets" xlink:label="loc_us-gaap_NoncurrentAssets_83483EC4A89068F269CED27CCBFFA437" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_D2D54C3775342942866ED27CCBFF55CF" xlink:to="loc_us-gaap_NoncurrentAssets_83483EC4A89068F269CED27CCBFFA437" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/SegmentReportingAndForeignOperationsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_04BB3B22B00B37AD3038806E1FD123EE" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable" xlink:label="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_44D16426F76694AB7986806E1FCB6D92" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_04BB3B22B00B37AD3038806E1FD123EE" xlink:to="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_44D16426F76694AB7986806E1FCB6D92" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="loc_us-gaap_StatementGeographicalAxis_13BE7235AAB185F42753806E1FCB3B0B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_44D16426F76694AB7986806E1FCB6D92" xlink:to="loc_us-gaap_StatementGeographicalAxis_13BE7235AAB185F42753806E1FCB3B0B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_C0E686A38F3881C23864806E1FCB5228_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementGeographicalAxis_13BE7235AAB185F42753806E1FCB3B0B" xlink:to="loc_us-gaap_SegmentGeographicalDomain_C0E686A38F3881C23864806E1FCB5228_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_C0E686A38F3881C23864806E1FCB5228" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementGeographicalAxis_13BE7235AAB185F42753806E1FCB3B0B" xlink:to="loc_us-gaap_SegmentGeographicalDomain_C0E686A38F3881C23864806E1FCB5228" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NonUsMember" xlink:label="loc_us-gaap_NonUsMember_256B7C9D946D661181F1806E1FD14103" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_C0E686A38F3881C23864806E1FCB5228" xlink:to="loc_us-gaap_NonUsMember_256B7C9D946D661181F1806E1FD14103" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SalesRevenueNet" xlink:label="loc_us-gaap_SalesRevenueNet_DA28CE0F21F45ADFFA81806E1FD129FB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_04BB3B22B00B37AD3038806E1FD123EE" xlink:to="loc_us-gaap_SalesRevenueNet_DA28CE0F21F45ADFFA81806E1FD129FB" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_ForeignSalesPercentOfTotalSales" xlink:label="loc_mmsi_ForeignSalesPercentOfTotalSales_DCE171A8C195ED7C0CD7806E1FD227E6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_04BB3B22B00B37AD3038806E1FD123EE" xlink:to="loc_mmsi_ForeignSalesPercentOfTotalSales_DCE171A8C195ED7C0CD7806E1FD227E6" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_ForeignSales" xlink:label="loc_mmsi_ForeignSales_B067C96B5470636915DE8073F2DE794E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_04BB3B22B00B37AD3038806E1FD123EE" xlink:to="loc_mmsi_ForeignSales_B067C96B5470636915DE8073F2DE794E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/SegmentReportingAndForeignOperationsOperatingIncomeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_F5F002044989FC62734680C0271479F2" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_7FDAD7DF753DA460748380C027132639" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_F5F002044989FC62734680C0271479F2" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_7FDAD7DF753DA460748380C027132639" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_7C0CDD59CE25AB12AA3880C02713AECF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_7FDAD7DF753DA460748380C027132639" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_7C0CDD59CE25AB12AA3880C02713AECF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_387F9BB92963DBE1979980C02713D0C9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_7C0CDD59CE25AB12AA3880C02713AECF" xlink:to="loc_us-gaap_SegmentDomain_387F9BB92963DBE1979980C02713D0C9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_387F9BB92963DBE1979980C02713D0C9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_7C0CDD59CE25AB12AA3880C02713AECF" xlink:to="loc_us-gaap_SegmentDomain_387F9BB92963DBE1979980C02713D0C9" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CardiovascularSegmentMember" xlink:label="loc_mmsi_CardiovascularSegmentMember_86AADA70354213F9C7D180C027134AB6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_387F9BB92963DBE1979980C02713D0C9" xlink:to="loc_mmsi_CardiovascularSegmentMember_86AADA70354213F9C7D180C027134AB6" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_EndoscopySegmentMember" xlink:label="loc_mmsi_EndoscopySegmentMember_CC1A53019EBF13D605EB80C027142EBE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_387F9BB92963DBE1979980C02713D0C9" xlink:to="loc_mmsi_EndoscopySegmentMember_CC1A53019EBF13D605EB80C027142EBE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SalesRevenueGoodsNet" xlink:label="loc_us-gaap_SalesRevenueGoodsNet_FBD82A6A9731CE0FC7F080C027145CBA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_F5F002044989FC62734680C0271479F2" xlink:to="loc_us-gaap_SalesRevenueGoodsNet_FBD82A6A9731CE0FC7F080C027145CBA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingExpenses" xlink:label="loc_us-gaap_OperatingExpenses_F8B71BFB02D76E5EC2AB80C02714DBF8" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_F5F002044989FC62734680C0271479F2" xlink:to="loc_us-gaap_OperatingExpenses_F8B71BFB02D76E5EC2AB80C02714DBF8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaap_OperatingIncomeLoss_5B59DB39013BBB6D9F9180C02714E95B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_F5F002044989FC62734680C0271479F2" xlink:to="loc_us-gaap_OperatingIncomeLoss_5B59DB39013BBB6D9F9180C02714E95B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NonoperatingIncomeExpense" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_43465B4E2E21FF3D46F980C02714BD2A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_F5F002044989FC62734680C0271479F2" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_43465B4E2E21FF3D46F980C02714BD2A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_D29FB4143C7024DA0D0480C0271479A1" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_F5F002044989FC62734680C0271479F2" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_D29FB4143C7024DA0D0480C0271479A1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_A88F147A7A8DE49C4B4580C02714559F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_F5F002044989FC62734680C0271479F2" xlink:to="loc_us-gaap_NetIncomeLoss_A88F147A7A8DE49C4B4580C02714559F" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/SegmentReportingAndForeignOperationsSalesByBusinessSegmentDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems" xlink:label="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_66CD2A604C287A3ED9FD80C0271D59DA" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable" xlink:label="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_44FC8DCDD2676EEC7D2A80C0271C7316" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_66CD2A604C287A3ED9FD80C0271D59DA" xlink:to="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_44FC8DCDD2676EEC7D2A80C0271C7316" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_94186BF06C3FC57D789580C0271C6E9D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_44FC8DCDD2676EEC7D2A80C0271C7316" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_94186BF06C3FC57D789580C0271C6E9D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_CE9E9F5ED17CA306B3EF80C0271C8157_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_94186BF06C3FC57D789580C0271C6E9D" xlink:to="loc_us-gaap_SegmentDomain_CE9E9F5ED17CA306B3EF80C0271C8157_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_CE9E9F5ED17CA306B3EF80C0271C8157" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_94186BF06C3FC57D789580C0271C6E9D" xlink:to="loc_us-gaap_SegmentDomain_CE9E9F5ED17CA306B3EF80C0271C8157" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CardiovascularSegmentMember" xlink:label="loc_mmsi_CardiovascularSegmentMember_7982AF950ED980CE2FFE80C0271C39CC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_CE9E9F5ED17CA306B3EF80C0271C8157" xlink:to="loc_mmsi_CardiovascularSegmentMember_7982AF950ED980CE2FFE80C0271C39CC" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_EndoscopySegmentMember" xlink:label="loc_mmsi_EndoscopySegmentMember_1746828DFED25909F92A80C0271C5504" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_CE9E9F5ED17CA306B3EF80C0271C8157" xlink:to="loc_mmsi_EndoscopySegmentMember_1746828DFED25909F92A80C0271C5504" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductOrServiceAxis" xlink:label="loc_us-gaap_ProductOrServiceAxis_D079FDBB664FE2B000DA80C0271C29CE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_44FC8DCDD2676EEC7D2A80C0271C7316" xlink:to="loc_us-gaap_ProductOrServiceAxis_D079FDBB664FE2B000DA80C0271C29CE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_D6A656D1775CE0AE251880C0271CBF9C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ProductOrServiceAxis_D079FDBB664FE2B000DA80C0271C29CE" xlink:to="loc_us-gaap_ProductsAndServicesDomain_D6A656D1775CE0AE251880C0271CBF9C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_D6A656D1775CE0AE251880C0271CBF9C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ProductOrServiceAxis_D079FDBB664FE2B000DA80C0271C29CE" xlink:to="loc_us-gaap_ProductsAndServicesDomain_D6A656D1775CE0AE251880C0271CBF9C" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_StandAloneDevicesMember" xlink:label="loc_mmsi_StandAloneDevicesMember_922F57E4797EB15D909580C0271C5364" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_D6A656D1775CE0AE251880C0271CBF9C" xlink:to="loc_mmsi_StandAloneDevicesMember_922F57E4797EB15D909580C0271C5364" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CustomKitAndProceduresTraysMember" xlink:label="loc_mmsi_CustomKitAndProceduresTraysMember_F9A174A6796CC10CA53880C0271C996F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_D6A656D1775CE0AE251880C0271CBF9C" xlink:to="loc_mmsi_CustomKitAndProceduresTraysMember_F9A174A6796CC10CA53880C0271C996F" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_InflationDevicesMember" xlink:label="loc_mmsi_InflationDevicesMember_9755DECD7390AE7D668D80C0271C09B2" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_D6A656D1775CE0AE251880C0271CBF9C" xlink:to="loc_mmsi_InflationDevicesMember_9755DECD7390AE7D668D80C0271C09B2" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_CathetersMember" xlink:label="loc_mmsi_CathetersMember_0264741FE0A0A13DE44C80C0271D63DA" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_D6A656D1775CE0AE251880C0271CBF9C" xlink:to="loc_mmsi_CathetersMember_0264741FE0A0A13DE44C80C0271D63DA" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_EmbolizationDevicesMember" xlink:label="loc_mmsi_EmbolizationDevicesMember_BF9ECA3FFAD6446E8E0080C0271D32D7" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_D6A656D1775CE0AE251880C0271CBF9C" xlink:to="loc_mmsi_EmbolizationDevicesMember_BF9ECA3FFAD6446E8E0080C0271D32D7" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_ElectrophysiologyMember" xlink:label="loc_mmsi_ElectrophysiologyMember_78F510C54B28D28E935480C0271DED10" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_D6A656D1775CE0AE251880C0271CBF9C" xlink:to="loc_mmsi_ElectrophysiologyMember_78F510C54B28D28E935480C0271DED10" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_EndoscopyDevicesMember" xlink:label="loc_mmsi_EndoscopyDevicesMember_6AFB82580AD3EF472C5380C0271D7246" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_D6A656D1775CE0AE251880C0271CBF9C" xlink:to="loc_mmsi_EndoscopyDevicesMember_6AFB82580AD3EF472C5380C0271D7246" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_SalesByBusinessSegmentChangeCurrentYearVsPriorYear" xlink:label="loc_mmsi_SalesByBusinessSegmentChangeCurrentYearVsPriorYear_A6E4DEAF4F94FEE1FAC880C0271D58CA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_66CD2A604C287A3ED9FD80C0271D59DA" xlink:to="loc_mmsi_SalesByBusinessSegmentChangeCurrentYearVsPriorYear_A6E4DEAF4F94FEE1FAC880C0271D58CA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SalesRevenueGoodsNet" xlink:label="loc_us-gaap_SalesRevenueGoodsNet_D228CE9987230983C62780C0271D9F53" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_66CD2A604C287A3ED9FD80C0271D59DA" xlink:to="loc_us-gaap_SalesRevenueGoodsNet_D228CE9987230983C62780C0271D9F53" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.merit.com/role/SegmentReportingAndForeignOperationsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/SubsequentEvents" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.merit.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SubsequentEventLineItems" xlink:label="loc_us-gaap_SubsequentEventLineItems_F77FCECB5FDCF66D6F6980B5F1040331" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SubsequentEventTable" xlink:label="loc_us-gaap_SubsequentEventTable_CC6AD396182A2562C0E480B5F103652E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_F77FCECB5FDCF66D6F6980B5F1040331" xlink:to="loc_us-gaap_SubsequentEventTable_CC6AD396182A2562C0E480B5F103652E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CounterpartyNameAxis" xlink:label="loc_us-gaap_CounterpartyNameAxis_9FC1A29ACCA5E839CF0B80B5F103189C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_CC6AD396182A2562C0E480B5F103652E" xlink:to="loc_us-gaap_CounterpartyNameAxis_9FC1A29ACCA5E839CF0B80B5F103189C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C017CED2104347C1075880B5F10357EB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CounterpartyNameAxis_9FC1A29ACCA5E839CF0B80B5F103189C" xlink:to="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C017CED2104347C1075880B5F10357EB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C017CED2104347C1075880B5F10357EB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CounterpartyNameAxis_9FC1A29ACCA5E839CF0B80B5F103189C" xlink:to="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C017CED2104347C1075880B5F10357EB" xlink:type="arc" />
    <link:loc xlink:href="mmsi-20161231.xsd#mmsi_ArgonMedicalDevicesandCatheterConnectionsInc.Member" xlink:label="loc_mmsi_ArgonMedicalDevicesandCatheterConnectionsInc.Member_B5D2E0986B51401DD10C80C005DAC099" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_C017CED2104347C1075880B5F10357EB" xlink:to="loc_mmsi_ArgonMedicalDevicesandCatheterConnectionsInc.Member_B5D2E0986B51401DD10C80C005DAC099" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_55127A72B1A06EE367D680B5F104E306" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_CC6AD396182A2562C0E480B5F103652E" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_55127A72B1A06EE367D680B5F104E306" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_24E6EA8383332C52365680B5F104825B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_55127A72B1A06EE367D680B5F104E306" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_24E6EA8383332C52365680B5F104825B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_24E6EA8383332C52365680B5F104825B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_55127A72B1A06EE367D680B5F104E306" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_24E6EA8383332C52365680B5F104825B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_D3AA66384C973890C45280B5F104C4A6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_24E6EA8383332C52365680B5F104825B" xlink:to="loc_us-gaap_SubsequentEventMember_D3AA66384C973890C45280B5F104C4A6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PaymentsToAcquireProductiveAssets" xlink:label="loc_us-gaap_PaymentsToAcquireProductiveAssets_7A9A4A50DB23EFA9F92A80BCA16C2F2A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_F77FCECB5FDCF66D6F6980B5F1040331" xlink:to="loc_us-gaap_PaymentsToAcquireProductiveAssets_7A9A4A50DB23EFA9F92A80BCA16C2F2A" xlink:type="arc" />
  </link:definitionLink>
</link:linkbase>





