<SUBMISSION>
<ACCESSION-NUMBER>0001022079-06-000079
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20060701
<FILING-DATE>20060705
<DATE-OF-FILING-DATE-CHANGE>20060705
<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>PFEIFFER GARY M
<CIK>0001127304
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>001-12215
<FILM-NUMBER>06944716
</FILING-VALUES>
<BUSINESS-ADDRESS>
<PHONE>3027733854
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>1007 MARKET ST
<CITY>WILMINGTON
<STATE>DE
<ZIP>19898
</MAIL-ADDRESS>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-07-01</periodOfReport>

    <issuer>
        <issuerCik>0001022079</issuerCik>
        <issuerName>QUEST DIAGNOSTICS INC</issuerName>
        <issuerTradingSymbol>DGX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001127304</rptOwnerCik>
            <rptOwnerName>PFEIFFER GARY M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O QUEST DIAGNOSTICS INCORPORATED</rptOwnerStreet1>
            <rptOwnerStreet2>1290 WALL STREET WEST</rptOwnerStreet2>
            <rptOwnerCity>LYNDHURST</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07071</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3334</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-07-01</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>408.88</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>408.88</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1876.54</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F3">Expiration date is not applicable since this is not a stock option.</footnote>
        <footnote id="F4">The total reflected in this column is inaccurate due to a computer program error.  Reporting Person has accrued a total of 2,872.43 Phantom Stock Units to date in his Deferred Compensation Account, including phantom stock units credited during the prior quarter as a result of unreported dividend reinvestment transactions.</footnote>
        <footnote id="F2">Exercise date is not appplicable as this is not a stock option.</footnote>
        <footnote id="F1">The Phantom Stock units were accrued on a periodic basis under the Quest Diagnostics Incorporated Deferred Compensation Plan and are to be settled in cash based on the then fair market value of the Company's Common Stock upon the Reporting Person's retirement.  Reporting Person's current term expires in May 2008 (the next annual meeting of shareholders of the Company).  The information was obtained from the plan administrator as of the current date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Leo C. Farrenkopf, Jr., atty-in-fact for Gary M. Pfeiffer</signatureName>
        <signatureDate>2006-07-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
