<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType><periodOfReport>2003-10-31</periodOfReport>
    <issuer>
        <issuerCik>0000010795</issuerCik>
        <issuerName>BECTON DICKINSON &amp; CO</issuerName>
        <issuerTradingSymbol>BDX</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001214330</rptOwnerCik>
            <rptOwnerName>PERRELLA JAMES E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O BECTON, DICKINSON AND COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BECTON DRIVE</rptOwnerStreet2>
            <rptOwnerCity>FRANKLIN LAKES</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07417</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>0</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther></reportingOwnerRelationship></reportingOwner><derivativeTable><derivativeTransaction><securityTitle><value>Rights to Common Stock Under 1996 Directors Deferral Plan</value></securityTitle><conversionOrExercisePrice><footnoteId id="F1"/></conversionOrExercisePrice><transactionDate><value>2003-10-31</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>381.18</value></transactionShares><transactionPricePerShare><value>36.40</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><footnoteId id="F2"/></exerciseDate><expirationDate><footnoteId id="F2"/></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>381.18</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>17418.38</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeTransaction></derivativeTable><footnotes><footnote id="F1">The securities convert to common stock on a one-for-one basis.</footnote><footnote id="F2">The securities are distributed following the termination of the reporting person's service as a director, on the date or dates specified by the reporting person.</footnote></footnotes><remarks/><ownerSignature><signatureName>Gary DeFazio, by power of attorney for James E. Perrella</signatureName><signatureDate>2003-11-03</signatureDate></ownerSignature></ownershipDocument>

