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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-12-21</periodOfReport>

    <issuer>
        <issuerCik>0000061986</issuerCik>
        <issuerName>MANITOWOC CO INC</issuerName>
        <issuerTradingSymbol>MTW</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001205085</rptOwnerCik>
            <rptOwnerName>JONES MAURICE D</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2400 SOUTH 44TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MANITOWOC</rptOwnerCity>
            <rptOwnerState>WI</rptOwnerState>
            <rptOwnerZipCode>54221-0066</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Sr.V.P., Gen Counsel and Sect.</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2007-12-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>22.5125</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>48.43</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>35730.0415</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3644.9666</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>RSVP 401k Plan</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">On September 10, 2007, the common stock of The Manitowoc Company, Inc. split 2-for-1.  This number consists of shares held under the Company's 401(k) plan (The Manitowoc Company, Inc. RSVP Profit Sharing Plan) including 234.7506 shares (split-adjusted) acquired in transactions occurring between 12/31/05 and 12/31/06, which are exempt from Section 16(b) pursuant to Rule 16b-3 and exempt from reporting pursuant to Rule 16a-3(f)(1)(i)(B).  The information in this report is based on a plan statement dated as of 12/31/06 and previously reported as 1,822.4833 shares, but has been adjusted to reflect the stock split on September 10, 2007.  From time to time the plan administrator collects maintenance fees related to the RSVP Plan, which may result in the number of shares held by a participant in the RSVP Plan declining by a marginal amount.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>MAURICEDJONES</signatureName>
        <signatureDate>2007-12-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
