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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-12-05</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001633313</rptOwnerCik>
            <rptOwnerName>Avoro Capital Advisors LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>110 GREENE STREET</rptOwnerStreet1>
            <rptOwnerStreet2>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>
            <officerTitle></officerTitle>
            <otherText>SEE REMARKS</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <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>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, $0.01 par value per share (&quot;Common Stock&quot;)</value>
            </securityTitle>
            <transactionDate>
                <value>2019-12-05</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2000000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>17.50</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>24500000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13516</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The securities reported herein are held on behalf of accounts managed by Avoro Capital Advisors LLC, a Delaware limited liability company (the &quot;Investment Manager&quot;) and Avoro Life Sciences 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">Restricted stock units held by Dr. Aghazadeh.</footnote>
    </footnotes>

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

    <ownerSignature>
        <signatureName>Avoro Capital Advisors LLC, by: /s/ Scott Epstein, its Chief Financial Officer &amp; Chief Compliance Officer</signatureName>
        <signatureDate>2019-12-09</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Behzad Aghazadeh</signatureName>
        <signatureDate>2019-12-09</signatureDate>
    </ownerSignature>
</ownershipDocument>
