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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
 F0ENxqvvBLXbogRP1JglCUIkcZto5AUvm4wdA2TUQxMSU8AHb1/a0um+WYyzj6Sj
 1C8/99OLRV5ixhj0eQKULQ==

<SEC-DOCUMENT>0001209726-09-000001.txt : 20090120
<SEC-HEADER>0001209726-09-000001.hdr.sgml : 20090119
<ACCEPTANCE-DATETIME>20090120162125
ACCESSION NUMBER:		0001209726-09-000001
CONFORMED SUBMISSION TYPE:	4/A
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20081211
FILED AS OF DATE:		20090120
DATE AS OF CHANGE:		20090120

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			SAVINI CARL A
		CENTRAL INDEX KEY:			0001209724

	FILING VALUES:
		FORM TYPE:		4/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-19119
		FILM NUMBER:		09534453

	MAIL ADDRESS:	
		STREET 1:		145 BRANDYWINE PKWY
		CITY:			WEST CHESTER
		STATE:			PA
		ZIP:			19380

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			CEPHALON INC
		CENTRAL INDEX KEY:			0000873364
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		IRS NUMBER:				232484489
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		41 MOORES ROAD
		CITY:			FRAZER
		STATE:			PA
		ZIP:			19355
		BUSINESS PHONE:		6103440200

	MAIL ADDRESS:	
		STREET 1:		41 MOORES ROAD
		CITY:			FRAZER
		STATE:			PA
		ZIP:			19355
</SEC-HEADER>
<DOCUMENT>
<TYPE>4/A
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2008-12-11</periodOfReport>

    <dateOfOriginalSubmission>2008-12-12</dateOfOriginalSubmission>

    <issuer>
        <issuerCik>0000873364</issuerCik>
        <issuerName>CEPHALON INC</issuerName>
        <issuerTradingSymbol>CEPH</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001209724</rptOwnerCik>
            <rptOwnerName>SAVINI CARL A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>41 MOORES ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>FRAZER</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19355</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP, Chief Admin. Off</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-12-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>15000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>58931</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2359</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Restricted stock award, pursuant to Company benefit plan, vesting 25% per year over 4 years.</footnote>
        <footnote id="F2">The total amount of securities beneficially owned following the reported transaction was inadvertently over-reported by 6,000 shares and therefore has been revised from 64,931 to 58,931.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Carolyn S. Iosca, Attorney-in-Fact For:  Carl A. Savini</signatureName>
        <signatureDate>2009-01-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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