<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3/A</documentType>

    <periodOfReport>2007-09-01</periodOfReport>

    <dateOfOriginalSubmission>2007-09-07</dateOfOriginalSubmission>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000010795</issuerCik>
        <issuerName>BECTON DICKINSON &amp; CO</issuerName>
        <issuerTradingSymbol>BDX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001411721</rptOwnerCik>
            <rptOwnerName>Bruder Scott P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O BECTON, DICKINSON AND COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>1 BECTON DRIVE</rptOwnerStreet2>
            <rptOwnerCity>FRANKLIN LAKES</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07417</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SrVP; Chief Technology Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4583</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents time vested units awarded under the Becton, Dickinson and Company 2004 Employee and Director Equity-Based Compensation Plan.  Includes 2,838 units that were omitted from the reporting person's original Form 3.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Patricia Walesiewicz, by power of attorney for Scott P. Bruder</signatureName>
        <signatureDate>2007-09-26</signatureDate>
    </ownerSignature>
</ownershipDocument>
