<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

<documentType>4/A</documentType><periodOfReport>2003-05-13</periodOfReport><dateOfOriginalSubmission>2003-05-13</dateOfOriginalSubmission>
<issuer><issuerCik>0000795551</issuerCik>
        <issuerName>THERAGENICS CORP</issuerName>
<issuerTradingSymbol>TGX</issuerTradingSymbol></issuer><reportingOwner><reportingOwnerId><rptOwnerCik>0001183377</rptOwnerCik>
            <rptOwnerName>DEAVENPORT EARNEST W JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
<reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>0</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther></reportingOwnerRelationship></reportingOwner><derivativeSecurity><securityTitle><value>Stock Option (Right to buy)</value></securityTitle><conversionOrExercisePrice><value>4.34</value></conversionOrExercisePrice><transactionDate><value>2003-05-13</value></transactionDate><deemedExecutionDate><value>2003-05-13</value></deemedExecutionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>15000</value></transactionShares><transactionValue><value>4.34</value></transactionValue><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>2004-05-13</value><footnoteId id="F1"/></exerciseDate><expirationDate><value>2013-05-13</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>15000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>63000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></derivativeSecurity><footnotes><footnote id="F1">The options vest in three equal annual installments beginning on May 13, 2004</footnote></footnotes><ownerSignature><signatureName>/s/ Lynn Rogers</signatureName><signatureDate>2003-05-05</signatureDate></ownerSignature></ownershipDocument>

