-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 BFi3IGDs3EHx0IpBCKd0cIKqYf7tsbq3awLHjGQyZBfzWx8ss8zDBMCe951+/Qf9
 k8q9sSViJlnwlVAid8LRyg==

<SEC-DOCUMENT>0001022079-05-000029.txt : 20050405
<SEC-HEADER>0001022079-05-000029.hdr.sgml : 20050405
<ACCEPTANCE-DATETIME>20050405164055
ACCESSION NUMBER:		0001022079-05-000029
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050401
FILED AS OF DATE:		20050405
DATE AS OF CHANGE:		20050405

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			QUEST DIAGNOSTICS INC
		CENTRAL INDEX KEY:			0001022079
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-MEDICAL LABORATORIES [8071]
		IRS NUMBER:				161387862
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		ONE MALCOLM AVE
		CITY:			TETERBORO
		STATE:			NJ
		ZIP:			07608
		BUSINESS PHONE:		2013935000

	MAIL ADDRESS:	
		STREET 1:		ONE MALCOLM AVE
		CITY:			TETERBORO
		STATE:			NJ
		ZIP:			07601

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	CORNING CLINICAL LABORATORIES INC
		DATE OF NAME CHANGE:	19960903

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			PFEIFFER GARY M
		CENTRAL INDEX KEY:			0001127304

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-12215
		FILM NUMBER:		05734491

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		3027733854

	MAIL ADDRESS:	
		STREET 1:		1007 MARKET ST
		CITY:			WILMINGTON
		STATE:			DE
		ZIP:			19898
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>c0001127304d20050405f4f.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-04-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <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>ONE MALCOLM AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>TETERBORO</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07608</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-04-01</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>133.17</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2005-04-01</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2005-04-01</value>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>133.17</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>133.17</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <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 common stock of Quest Diagnostics Incorporated (the &quot;Company&quot;) upon the Reporting Person's termination of services as a director of the Company.  Reporting Person's current term expires on May 10, 2005 (the next annual meeting of stockholders of the Company). The information was obtained from the plan administrator as of the current date.</footnote>
        <footnote id="F2">Exercise date is not appplicable as this is not a stock option.</footnote>
        <footnote id="F3">Expiration date is not applicable since this is not a stock option.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Sirisha Gummaregula</signatureName>
        <signatureDate>2005-04-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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