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

    <schemaVersion>X0201</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2004-04-14</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001233426</issuerCik>
        <issuerName>MILLSTREAM ACQUISITION CORP</issuerName>
        <issuerTradingSymbol>MSTM</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001019190</rptOwnerCik>
            <rptOwnerName>MHR CAPITAL PARTNERS LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>40 WEST 57TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2>24TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001284082</rptOwnerCik>
            <rptOwnerName>MHR ADVISORS LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>40 WEST 57TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2>24TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock, par value $.0001 per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>487001</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Common Stock Warrants (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>5.00</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2004-08-25</value>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2007-08-24</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>474001</value>
                    <footnoteId id="F4"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Of this amount, 153,667 shares of the Issuer's common stock, par value $.0001 per share (&quot;Shares&quot;), are included within 153,667 units (&quot;Units&quot;) held for the account of MHR Capital Partners, LP, a Delaware limited partnership (&quot;Capital Partners&quot;).  Units consist of one Share and two warrants to purchase Shares.  The warrants are not presently exercisable but only become exercisable at the later of the Issuer's completion of a business combination or August 25, 2004.</footnote>
        <footnote id="F2">These securities are held for the account of Capital Partners.  MHR Advisors LLC, a Delaware limited liability company (&quot;Advisors&quot;), is the general partner of Capital Partners.  Mark H. Rachesky, M.D. (&quot;Dr. Rachesky&quot;) is the managing member of Advisors.  In such capacity, Dr. Rachesky may be deemed to have voting and dispositive power over the Shares and other securities held for the account of Capital Partners.</footnote>
        <footnote id="F3">These warrants will become exercisable upon the later of the Issuer's completion of a business combination with a target business or August 25, 2004.</footnote>
        <footnote id="F4">Capital Partners and Advisors may be deemed to have an interest in the 474,001 warrants to purchase Shares held for the account of Capital Partners.  Of this amount, 307,334 warrants to purchase Shares are included within 153,667 Units held for the account of Capital Partners.  Units consist of one Share and two warrants to purchase Shares.  The warrants are not presently exercisable but only become exercisable at the later of the Issuer's completion of a business combination or August 25, 2004.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Hal Goldstein, as Vice President of MHR Advisors LLC, as General Partner of MHR Capital Partners LP</signatureName>
        <signatureDate>2004-04-20</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Hal Goldstein, as Vice President of MHR Advisors LLC</signatureName>
        <signatureDate>2004-04-20</signatureDate>
    </ownerSignature>
</ownershipDocument>

