<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-10-23</periodOfReport>

    <issuer>
        <issuerCik>0001009575</issuerCik>
        <issuerName>HLTH CORP</issuerName>
        <issuerTradingSymbol>HLTH</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000905448</rptOwnerCik>
            <rptOwnerName>WYGOD MARTIN J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>669 RIVER DR, CENTER 2</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ELMWOOD PARK</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07407</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chairman of the Board</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2007-10-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>35487</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>14.01</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7341584</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Shares include Restricted Stock granted on 10/23/2006 of which 45,513 shares have vested and remain outstanding and of which 99,000 shares vest on 10/23/2008 and 120,000 shares vest on 10/23/2009. Shares also include 150,000 shares of Restricted Stock granted on 01/27/2006 of which 50,000 have vested and remain outstanding and of which 50,000 will vest on each of 01/27/2008 and 01/27/2009.  As reported on this Form 4, 35,487 shares of the Restricted Stock that vested as of 10/23/2007 were withheld by HLTH Corporation in order to satisfy the minimum tax withholding requirement arising for the 10/23/2007 vesting.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Lewis H. Leicher, Attorney-in-Fact for Martin J. Wygod</signatureName>
        <signatureDate>2007-10-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
