-----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,
 AyZ0feRclNMnxPNtjAnheNxfzVnCgiA/JX+XMISfFGSjNx0LIiyyYEhMEvYZ/l9U
 kDmfpWXfMvK5u7yAtXYFKg==

<SEC-DOCUMENT>0001018952-05-000052.txt : 20050523
<SEC-HEADER>0001018952-05-000052.hdr.sgml : 20050523
<ACCEPTANCE-DATETIME>20050523164440
ACCESSION NUMBER:		0001018952-05-000052
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050520
FILED AS OF DATE:		20050523
DATE AS OF CHANGE:		20050523

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			KOS PHARMACEUTICALS INC
		CENTRAL INDEX KEY:			0001018952
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		IRS NUMBER:				650670898
		STATE OF INCORPORATION:			FL
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1001 BRICKELL BAY DR STE 25
		CITY:			MIAMI
		STATE:			FL
		ZIP:			33131
		BUSINESS PHONE:		3055773464

	MAIL ADDRESS:	
		STREET 1:		1001 BRICKELL BAY DRIVE STE 25
		CITY:			MIAMI
		STATE:			FL
		ZIP:			33131

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			KIRITSY CHRISTOPHER P
		CENTRAL INDEX KEY:			0001261156

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-22171
		FILM NUMBER:		05851718

	BUSINESS ADDRESS:	
		STREET 1:		C/O KOS PHARMACETUICALS INC
		STREET 2:		1001 BRICKELL BAY DRIVE 25TH FLOOR
		CITY:			MIAMI
		STATE:			FL
		ZIP:			33131
		BUSINESS PHONE:		3055773464
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-05-20</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001018952</issuerCik>
        <issuerName>KOS PHARMACEUTICALS INC</issuerName>
        <issuerTradingSymbol>KOSP</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001261156</rptOwnerCik>
            <rptOwnerName>KIRITSY CHRISTOPHER P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1></rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity></rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Executive VP and CFO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, $.01 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2005-05-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>19.5</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8000</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, $.01 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2005-05-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>55</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3000</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>19.5</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-05-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2013-01-22</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>51500</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Includes one share jointly owned with spouse.</footnote>
        <footnote id="F2">Includes 2,999 shares of Kos common stock acquired by reporting person in transactions exempt under Section 16 of the Exchange Act under the Kos 401(k) plan and the Employee Stock Purchase Plan.</footnote>
        <footnote id="F3">Part of an original grant of 85,000 options, exercisable in the following amounts on the following exercise dates:
21,250 on January 23, 2004
21,250 on January 23, 2005
21,250 on January 23, 2006
21,250 on January 23, 2007</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Juan F. Rodriguez, Attorney-in-Fact</signatureName>
        <signatureDate>2005-05-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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