<SUBMISSION>
<ACCESSION-NUMBER>0001022079-06-000064
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20060510
<FILING-DATE>20060512
<DATE-OF-FILING-DATE-CHANGE>20060512
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>QUEST DIAGNOSTICS INC
<CIK>0001022079
<ASSIGNED-SIC>8071
<IRS-NUMBER>161387862
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>ONE MALCOLM AVE
<CITY>TETERBORO
<STATE>NJ
<ZIP>07608
<PHONE>2013935000
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>ONE MALCOLM AVE
<CITY>TETERBORO
<STATE>NJ
<ZIP>07601
</MAIL-ADDRESS>
<FORMER-COMPANY>
<FORMER-CONFORMED-NAME>CORNING CLINICAL LABORATORIES INC
<DATE-CHANGED>19960903
</FORMER-COMPANY>
</ISSUER>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>HAGEMANN ROBERT
<CIK>0001222676
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>001-12215
<FILM-NUMBER>06836595
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>QUEST DIAGNOSTICS INC
<STREET2>ONE MALCOLM AVE
<CITY>TETERBORO
<STATE>NJ
<ZIP>07608
</BUSINESS-ADDRESS>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
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        <issuerName>QUEST DIAGNOSTICS INC</issuerName>
        <issuerTradingSymbol>DGX</issuerTradingSymbol>
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        <reportingOwnerAddress>
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            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>LYNDHURST</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07071</rptOwnerZipCode>
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        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
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            <officerTitle>SVP &amp; Chief Financial Officer</officerTitle>
            <otherText></otherText>
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                <natureOfOwnership>
                    <value>401k/SDCP</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
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        </nonDerivativeTransaction>
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    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
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            </securityTitle>
            <conversionOrExercisePrice>
                <value>6.585</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-05-11</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
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                <value></value>
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                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2002-07-31</value>
            </exerciseDate>
            <expirationDate>
                <value>2009-08-16</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
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                <transactionAcquiredDisposedCode>
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            <exerciseDate>
                <value>2000-08-16</value>
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            <expirationDate>
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            </expirationDate>
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                <underlyingSecurityTitle>
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                <directOrIndirectOwnership>
                    <value>D</value>
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                <transactionCode>A</transactionCode>
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                <value></value>
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                </transactionAcquiredDisposedCode>
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            <exerciseDate>
                <value>2007-05-11</value>
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                <value>2009-08-16</value>
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                <underlyingSecurityTitle>
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    <footnotes>
        <footnote id="F2">These underlying shares were acquired on a periodic basis by the trustee of the Company's tax qualified Profit Sharing (401(k) and/or Supplemental Deferred Compensation Plan.  The information was obtained from the plan administrator as of a recent date.  The number of shares is based on the account balance of the Company stock fund under the plan (which includes some money market instruments) divided by the market price of the Company's stock as of that date.</footnote>
        <footnote id="F1">On June 20, 2005, the Company effected a 2-for-1 stock split of its Common Stock in the form of a 100% stock dividend.  All prior holdings, including stock options, have been adjusted to reflect the stock split.</footnote>
        <footnote id="F3">this is a database error.  There are no exercisable options remaining on this grant.</footnote>
        <footnote id="F4">This is a database error.  There are no exercisable options remaining on this grant.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Leo C. Farrenkopf, Jr., atty-in-fact for Robert A. Hagemann</signatureName>
        <signatureDate>2006-05-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
