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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-02-10</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000831327</issuerCik>
        <issuerName>IMPERIAL SUGAR CO /NEW/</issuerName>
        <issuerTradingSymbol>IPSU</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000806085</rptOwnerCik>
            <rptOwnerName>LEHMAN BROTHERS HOLDINGS INC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>745 SEVENTH AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></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>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-02-10</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>68559</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3315715</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Received as a final distribution of the Issuer's Common Stock, effective dated February 9, 2006, under the Issuer's Second Amended and Restated Joint Plan of Reorganization dated June 5, 2001, as further described in the Reporting Person's Schedule 13D (as amended) filed with the Commission in respect of the Issuer's Common Stock.</footnote>
        <footnote id="F2">This form is a joint filing with Lehman Brothers Inc., a wholly owned subsidiary of the Reporting Person and a broker-dealer registered under Section 15 of the 1934 Act.</footnote>
    </footnotes>

    <remarks>JOINT FILER INFORMATION

Title of Security: Common Stock
Issuer &amp; Ticker Symbol: Imperial Sugar Company (IPSU)
Designated Filer: Lehman Brothers Holdings Inc.
Other Joint Filer(s):
Lehman Brothers Inc.
745 Seventh Avenue
New York, New York 10019
Date of Event Requiring Statement:
February 10, 2006
Signature on behalf of
other above filer:
/s/ Barrett S. DiPaolo
Senior Vice President</remarks>

    <ownerSignature>
        <signatureName>/s/ Barrett S. DiPaolo, Vice President</signatureName>
        <signatureDate>2006-03-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
