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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-03-08</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001100441</issuerCik>
        <issuerName>RTI SURGICAL, INC.</issuerName>
        <issuerTradingSymbol>RTIX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001754464</rptOwnerCik>
            <rptOwnerName>Bartolucci Ryan M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O RTI SURGICAL, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>11621 RESEARCH CIRCLE</rptOwnerStreet2>
            <rptOwnerCity>ALACHUA</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>32615</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP Corporate Controller</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2019-03-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>18734</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Option to purchase common stock $.001 par value</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>4.6</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2019-03-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>17202</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.6</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <value>2028-09-25</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>17202</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">On March 8, 2019, pursuant to the Master Transaction Agreement, by and among the Issuer, RTI Surgical, Inc., a Delaware corporation (&quot;Old RTI&quot;), PS Spine Holdco, LLC, a Delaware limited liability company (the &quot;Member&quot;), and Bears Merger Sub, Inc., a Delaware corporation (the &quot;Merger Sub&quot;): (a) the Merger Sub merged with and into Old RTI, with Old RTI surviving as a wholly-owned subsidiary of the Issuer (the &quot;Merger&quot;); (b) the Member contributed all of the issued and outstanding membership interests of Paradigm Spine, LLC, a Delaware limited liability company and wholly owned subsidiary of the Member, to the Issuer; and (c) the Issuer was renamed &quot;RTI Surgical Holdings, Inc.&quot;</footnote>
        <footnote id="F2">Pursuant to the Master Transaction Agreement, at the effective time of the Merger: (a) each issued and outstanding share of common stock of Old RTI converted automatically into one share of the Issuer's common stock; (b) each issued and outstanding share of Series A Convertible Preferred Stock of Old RTI converted automatically into one share of the Issuer's Series A Convertible Preferred Stock; and (c) each stock option and restricted stock award granted by Old RTI converted into a stock option or restricted stock award, as applicable, of the Issuer with respect to an equivalent number of shares of the Issuer's common stock on the same terms and conditions as were applicable prior to the Closing. This report reflects the beneficial ownership of the reporting person at the time of the consummation of the Merger and does not include the securities of the Issuer acquired by the reporting person upon the consummation of the Merger.</footnote>
        <footnote id="F3">The reporting person will file a Form 4 reflecting his acquisition of the Issuer's securities in connection with the consummation of the Mergers.</footnote>
        <footnote id="F4">Total includes 16,734 shares of restricted stock that will vest on; 2,717 shares on each of 9/25/2019 and 9/25/2020 and 2,718 shares on 9/25/2021, 2,861 shares on each of 2/26/2020 and 2/26/2021 and 2,860 shares on 2/26/2022.</footnote>
        <footnote id="F5">The options will become exercisable as to 3,440 shares on each of 9/25/2019, 9/25/2020, 9/25/2021 and 3,441 shares on each of 9/25/2022 and 9/25/2023.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Ryan M. Bartolucci</signatureName>
        <signatureDate>2019-03-11</signatureDate>
    </ownerSignature>
</ownershipDocument>
