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

    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-03-19</periodOfReport>

    <issuer>
        <issuerCik>0000091388</issuerCik>
        <issuerName>SMITHFIELD FOODS INC</issuerName>
        <issuerTradingSymbol>SFD</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001261298</rptOwnerCik>
            <rptOwnerName>MURPHY STRATTON K</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>P.O. BOX 1087</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ROSE HILL</rptOwnerCity>
            <rptOwnerState>NC</rptOwnerState>
            <rptOwnerZipCode>28458</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2004-03-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>G</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>33300</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1114995</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2004-03-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>266700</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>848295</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2004-03-19</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F3"/>
                <footnoteId id="F4"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>264033</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2667</value>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By SKM Legacy LLC</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The Reporting Person transferred 33,300 shares of Smithfield Foods, Inc. common stock (&quot;Common Stock&quot;) to SKM Legacy Trust for no consideration on March 16, 2004.  The Reporting Person does not exercise investment control over SMK Legacy Trust.  The Reporting Person disclaims beneficial ownership of the shares of Common Stock owned by SKM Legacy Trust.</footnote>
        <footnote id="F2">The Reporting Person transferred 266,700 shares of Common Stock to SKM Legacy LLC, a Delaware limited liability company, in exchange for the Class A and Class B units representing 100% of the ownership interest of SKM Legacy LLC on March 16, 2004.  SKM Legacy LLC was wholly owned by the Reporting Person until March 19, 2004, as described below in footnote 3.  The transfer from the Reporting Person to SKM Legacy LLC was a change in the form of beneficial ownership, from direct to indirect, which is exempt from Section 16 pursuant to Rule 16a-13 under the Securities Exchange Act of 1934.</footnote>
        <footnote id="F3">On March 19, 2004, the Reporting Person transferred 100%, subject to subsequent adjustment, of the Class B limited liability company interests of SKM Legacy LLC, which represent 99% of the Reporting Person's pecuniary interest in the shares of Common Stock held by SKM Legacy LLC.  At the time of the transfer, the shares of Common Stock held by SKM Legacy LLC represented approximately 77% of the value of the total assets held by SKM Legacy LLC.  The SKM Legacy LLC Class B interests were transferred to SKM Legacy Trust in exchange for a promissory note in the amount of $5.0 million, which amount is subject to adjustment based on a valuation prepared by an independent third party.  The Reporting Person retains all of the Class A limited liability interests in SKM Legacy LLC, which provide the Reporting Person with a 1% pecuniary interest in the shares of Common Stock held by SKM Legacy LLC</footnote>
        <footnote id="F4">(continuation of prior footnote)  and the power to transfer the Class A interests in SKM Legacy LLC and to change the manager of SKM Legacy LLC.  Dispositive power over the shares of Common Stock owned by SKM Legacy LLC is held by an independent manager, as required under the SKM Legacy LLC operating agreement.</footnote>
        <footnote id="F5">This amount reflects the Reporting Person's ownership of 1% of the pecuniary interest of the shares of Common Stock owned by SKM Legacy LLC.</footnote>
    </footnotes>

    <remarks>The reporting person may be deemed to be a member of a &quot;group&quot; with Wendell H. Murphy, Wendell H. Murphy, Jr., Harry D. Murphy, Wendy Murphy Crumpler, Joyce Murphy Minchew, Marc D. Murphy and Angela Norman Brown for purposes of Section 13(d) of the Exchange Act.</remarks>

    <ownerSignature>
        <signatureName>Mark Roberts (attorney-in-fact)</signatureName>
        <signatureDate>2004-03-23</signatureDate>
    </ownerSignature>
</ownershipDocument>

