<SUBMISSION>
<ACCESSION-NUMBER>0001022079-06-000024
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20060215
<FILING-DATE>20060217
<DATE-OF-FILING-DATE-CHANGE>20060217
<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>ZEWE DAVID M
<CIK>0001222680
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>001-12215
<FILM-NUMBER>06629736
</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>c0001222680d20060217f4f.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-02-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001222680</rptOwnerCik>
            <rptOwnerName>ZEWE DAVID M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1290 WALL STREET WEST</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>LYNDHURST</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07071</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP, Diagnostic Testing Ops</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>37328</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4928</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>401K/SDCP</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Options (Right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>52.235</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-02-15</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>63334</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2007-02-15</value>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2013-02-15</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>63334</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>63334</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Certain of these shares are subject to restrictions on transfer, the possibility of forfeiture and/or certain other terms contained in the underlying stock agreements and related plan documents.  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.  This amount also includes exempt purchases made under the Company's stock purchase plan since the date of the last filing on Form 4.</footnote>
        <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 obtain 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="F3">The option vests in three equal annual installments beginning on the first anniversary of this grant.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Sirisha Gummaregula</signatureName>
        <signatureDate>2006-02-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
