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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2020-06-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000722830</issuerCik>
        <issuerName>IMMUNOMEDICS INC</issuerName>
        <issuerTradingSymbol>IMMU</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001701815</rptOwnerCik>
            <rptOwnerName>Aghazadeh Behzad</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O AVORO CAPITAL ADVISORS LLC</rptOwnerStreet1>
            <rptOwnerStreet2>110 GREENE STREET, SUITE 800</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10012</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>See Remarks</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001633313</rptOwnerCik>
            <rptOwnerName>Avoro Capital Advisors LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O AVORO CAPITAL ADVISORS LLC</rptOwnerStreet1>
            <rptOwnerStreet2>110 GREENE STREET, SUITE 800</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10012</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>See Remarks</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, $0.01 par value per share (''Common Stock'')</value>
            </securityTitle>
            <transactionDate>
                <value>2020-06-18</value>
                <footnoteId id="F3"/>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3718</value>
                    <footnoteId id="F4"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>17234</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>100000</value>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>26250000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>33.62</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2020-06-18</value>
                <footnoteId id="F3"/>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>6540</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2021-06-18</value>
                <footnoteId id="F6"/>
            </exerciseDate>
            <expirationDate>
                <value>2030-06-18</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, par value $0.01 per share</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>6540</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6540</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Such securities are held on behalf of accounts managed by Avoro Capital Advisors LLC (formerly venBio Select Advisor LLC), a Delaware limited liability company (the &quot;Investment Manager&quot;) and Avoro Life Sciences Fund LLC (formerly venBio Select Fund LLC), a Delaware limited liability company, a fund managed by the Investment Manager. Behzad Aghazadeh (&quot;Dr. Aghazadeh,&quot; and together with the Investment Manager, the &quot;Reporting Persons&quot;) serves as the portfolio manager and controlling person of the Investment Manager.</footnote>
        <footnote id="F2">The filing of this statement shall not be deemed an admission that either of the Reporting Persons is the beneficial owner of the securities reported herein for purposes of Section 16 of the Securities Act of 1934, as amended, or otherwise. Each of the Reporting Persons expressly disclaims beneficial ownership of the securities reported herein except to the extent of its or his pecuniary interest therein.</footnote>
        <footnote id="F3">Such grants of restricted stock units (&quot;RSUs&quot;) and stock options were made automatically pursuant to the Issuer's compensation policy for non-employee directors as of the date of the Issuer's 2020 annual meeting of stockholders, which occurred on June 18, 2020.</footnote>
        <footnote id="F4">Includes RSUs held by Dr. Aghazadeh that represent a contingent right to receive one share of the Issuer's common stock. The RSUs shall vest on the first anniversary of the date of grant, subject to Dr. Aghazadeh's continued service as a director of the Issuer.</footnote>
        <footnote id="F5">Includes RSUs held by Dr. Aghazadeh, granted on March 20, 2020. 1/3 of the RSUs vest on each of the first, second and third anniversary of the date of grant, subject to Dr. Aghazadeh's continued service as the Issuer's Executive Chairman.</footnote>
        <footnote id="F6">The stock options vest on the first anniversary of the date of grant, subject to Dr. Aghazadeh's continued service as a director of the Issuer.</footnote>
    </footnotes>

    <remarks>The Investment Manager may be deemed a director by deputization of Immunomedics, Inc. by virtue of the fact that Dr. Aghazadeh currently serves on the board of directors of the Issuer.</remarks>

    <ownerSignature>
        <signatureName>/s/ Behzad Aghazadeh</signatureName>
        <signatureDate>2020-06-22</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Avoro Capital Advisors LLC, by: /s/ Behzad Aghazadeh, authorized signatory</signatureName>
        <signatureDate>2020-06-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
