<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><Version>2.4.0.8</Version><ReportLongName>1070 - Disclosure - LONG-TERM DEBT</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column FlagID="0"><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><CurrencyCode /><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName /><CurrencySymbol /><contextRef><ContextID>D2013Q2YTD</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0000834162</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2013-01-01T00:00:00</PeriodStartDate><PeriodEndDate>2013-06-30T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS /><CurrencyCode /><OriginalCurrencyCode /></MCU><CurrencySymbol /><Labels><Label Key="CalendarSupplement" Id="0" Label="6 Months Ended" /><Label Key="Calendar" Id="1" Label="Jun. 30, 2013" /></Labels></Column></Columns><Rows><Row FlagID="0"><Id>1</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>1</Level><ElementName>us-gaap_DebtDisclosureAbstract</ElementName><ElementPrefix>us-gaap_</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>LONG-TERM DEBT</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>2</Level><ElementName>us-gaap_DebtDisclosureTextBlock</ElementName><ElementPrefix>us-gaap_</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>terseLabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="D2013Q2YTD" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div style="font-size:10.0pt;font-family:Times New Roman;"&gt;
&lt;p style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&lt;b&gt;NOTE 7&amp;#8212;LONG-TERM DEBT&lt;/b&gt;&lt;/font&gt;&lt;/p&gt;
&lt;p style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;Long-term debt obligations are summarized as follows:&lt;/font&gt;&lt;/p&gt;
&lt;div style="POSITION: relative; PADDING-BOTTOM: 0pt; PADDING-LEFT: 0pt; WIDTH: 70%; PADDING-RIGHT: 0pt; MARGIN-LEFT: 15%; PADDING-TOP: 0pt;"&gt;
&lt;p style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&lt;!-- COMMAND=ADD_TABLEWIDTH,"100%" --&gt;&lt;/font&gt;&lt;/p&gt;
&lt;!-- User-specified TAGGED TABLE --&gt;
&lt;div align="center"&gt;
&lt;table border="0" cellspacing="0" cellpadding="0" width="100%" style="text-align:left;"&gt;

&lt;tr style="padding:0;"&gt;&lt;!-- TABLE COLUMN WIDTHS SET --&gt;
&lt;td style="FONT-FAMILY: times;" align="left"&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" width="12"&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" width="7" align="right"&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" width="51"&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" width="12"&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" width="7" align="right"&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" width="64"&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" width="12"&gt;&lt;/td&gt;&lt;!-- TABLE COLUMN WIDTHS END --&gt;&lt;/tr&gt;
&lt;tr style="padding:0;" valign="bottom"&gt;
&lt;th style="FONT-FAMILY: times;" align="left"&gt;&lt;font size="2"&gt;&amp;#160;&lt;/font&gt;&lt;br /&gt;&lt;/th&gt;
&lt;th style="FONT-FAMILY: times;"&gt;&lt;font size="1"&gt;&amp;#160;&lt;/font&gt;&lt;/th&gt;
&lt;th style="BORDER-BOTTOM: #000000 1pt solid; FONT-FAMILY: times;" colspan="2" align="center"&gt;&lt;font size="1"&gt;&lt;b&gt;June&amp;#160;30,&lt;br /&gt;
2013&lt;/b&gt;&lt;/font&gt;&lt;/th&gt;
&lt;th style="FONT-FAMILY: times;"&gt;&lt;font size="1"&gt;&amp;#160;&lt;/font&gt;&lt;/th&gt;
&lt;th style="BORDER-BOTTOM: #000000 1pt solid; FONT-FAMILY: times;" colspan="2" align="center"&gt;&lt;font size="1"&gt;&lt;b&gt;December&amp;#160;31,&lt;br /&gt;
2012&lt;/b&gt;&lt;/font&gt;&lt;/th&gt;
&lt;th style="FONT-FAMILY: times;"&gt;&lt;font size="1"&gt;&amp;#160;&lt;/font&gt;&lt;/th&gt;&lt;/tr&gt;
&lt;tr style="padding:0;" valign="bottom"&gt;
&lt;th style="FONT-FAMILY: times;" align="left"&gt;&lt;font size="1"&gt;&amp;#160;&lt;/font&gt;&lt;br /&gt;&lt;/th&gt;
&lt;th style="FONT-FAMILY: times;"&gt;&lt;font size="1"&gt;&amp;#160;&lt;/font&gt;&lt;/th&gt;
&lt;th style="FONT-FAMILY: times;" colspan="5" align="center"&gt;&lt;font size="1"&gt;&lt;b&gt;(in thousands)&lt;/b&gt;&lt;/font&gt;&lt;br /&gt;&lt;/th&gt;
&lt;th style="FONT-FAMILY: times;"&gt;&lt;font size="1"&gt;&amp;#160;&lt;/font&gt;&lt;/th&gt;&lt;/tr&gt;
&lt;tr style="padding:0;" valign="bottom" bgcolor="#CCEEFF"&gt;
&lt;td style="FONT-FAMILY: times;"&gt;
&lt;p style="TEXT-INDENT: -10pt; FONT-FAMILY: times; MARGIN-LEFT: 10pt;"&gt;&lt;font size="2"&gt;11.5% Senior Secured Second Lien Notes (net of unamortized discount of $12,889 and $13,948 in 2013 and 2012, respectively)&lt;/font&gt;&lt;/p&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" align="right"&gt;&lt;font size="2"&gt;$&lt;/font&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" align="right"&gt;&lt;font size="2"&gt;557,775&lt;/font&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" align="right"&gt;&lt;font size="2"&gt;$&lt;/font&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" align="right"&gt;&lt;font size="2"&gt;556,716&lt;/font&gt;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr style="padding:0; FONT-SIZE: 1.5pt;" valign="top"&gt;
&lt;td style="FONT-FAMILY: times;" valign="bottom"&gt;&amp;#160;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" valign="bottom"&gt;&amp;#160;&lt;/td&gt;
&lt;td style="BORDER-BOTTOM: #000000 2.25pt double; FONT-FAMILY: times;" valign="bottom" colspan="2" align="right"&gt;&amp;#160;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" valign="bottom"&gt;&amp;#160;&lt;/td&gt;
&lt;td style="BORDER-BOTTOM: #000000 2.25pt double; FONT-FAMILY: times;" valign="bottom" colspan="2" align="right"&gt;&amp;#160;&lt;/td&gt;
&lt;td style="FONT-FAMILY: times;" valign="bottom"&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;&lt;/table&gt;&lt;/div&gt;
&lt;!-- end of user-specified TAGGED TABLE --&gt;&lt;/div&gt;
&lt;p style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&lt;b&gt;&lt;i&gt;Senior Secured Second Lien Notes&lt;/i&gt;&lt;/b&gt;&lt;/font&gt;&lt;/p&gt;
&lt;p style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;On August&amp;#160;1, 2011, we completed the offering of $565.0&amp;#160;million 11.5% Senior Secured Second Lien Notes due August&amp;#160;1, 2019 (the "Notes") at an issue price equal to 97% of the aggregate principal amount of the Notes. The Notes were issued pursuant to an indenture, dated as of August&amp;#160;1, 2011 (the "Indenture"), among the Company, Mountaineer Park,&amp;#160;Inc., Presque Isle Downs,&amp;#160;Inc., Scioto Downs, Inc. (each, a wholly-owned subsidiary of the Company and as a guarantor, the "Guarantors") and Wilmington Trust, National Association, as Trustee and as Collateral Agent.&lt;/font&gt;&lt;/p&gt;
&lt;p style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;The Notes mature on August&amp;#160;1, 2019, with interest payable semi-annually in arrears on February&amp;#160;1 and August&amp;#160;1 of each year. Until and including the interest payment paid on August&amp;#160;1, 2013, interest was payable, at the election of the Company, (i)&amp;#160;entirely in cash or (ii)&amp;#160;at a rate of 10.50% in cash and a rate of 1.00% paid in kind ("PIK") by increasing the principal amount of the outstanding Notes or by issuing additional PIK Notes, as defined in the Indenture. The interest payments due on February&amp;#160;1, 2012 and August&amp;#160;1, 2012 were satisfied in cash and PIK Notes, resulting in the issuance of $5.6&amp;#160;million of additional Notes during 2012, increasing the total Notes outstanding to $570.7&amp;#160;million. We satisfied our February&amp;#160;1, 2013 and August&amp;#160;1, 2013 interest payments entirely in cash.&lt;/font&gt;&lt;/p&gt;
&lt;p style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;The Notes and the guarantees are the Company's and the Guarantors' senior secured obligations and are jointly and severally, fully, and unconditionally guaranteed by the Guarantors, as well as future subsidiaries, other than our immaterial subsidiaries and unrestricted subsidiaries, as defined in the Indenture. The Notes and the guarantees rank equally in right of payment with all of the Company's and the Guarantors' existing and future senior debt and senior in right of payment to all of the Company's and the Guarantors' future subordinated debt. The Notes and the guarantees will be effectively junior to any of the Company's and the Guarantors' existing and future debt that is secured by senior or prior liens on the collateral, including indebtedness under the Company's new senior secured revolving credit facility, as discussed below, to the extent of the value of the collateral securing such obligations. The Notes and the guarantees will be structurally subordinated to all existing and future liabilities of the Company's subsidiaries that do not guarantee the Notes.&lt;/font&gt;&lt;/p&gt;
&lt;p style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;The Notes are secured by a second priority lien on substantially all of the assets of the Company and the Guarantors, other than excluded property, as defined in the Indenture.&lt;/font&gt;&lt;/p&gt;
&lt;p style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&lt;b&gt;&lt;i&gt;Credit Facility&lt;/i&gt;&lt;/b&gt;&lt;/font&gt;&lt;/p&gt;
&lt;p style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;On August&amp;#160;1, 2011, we entered into a senior secured revolving credit facility (the "Credit Facility") with a borrowing availability of $20.0&amp;#160;million and a maturity date of August&amp;#160;1, 2016. There were no borrowings outstanding as of June&amp;#160;30, 2013 or December&amp;#160;31, 2012.&lt;/font&gt;&lt;/p&gt;
&lt;p style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;The Credit Facility is secured by substantially the same assets securing the Notes (and including securities of the Company's subsidiaries to the extent permitted by law). Borrowings under the Credit Facility are guaranteed by all of our existing and future domestic restricted subsidiaries. The security interest in the collateral that secures the Credit Facility is senior to the security interest in the collateral that secures the Notes.&lt;/font&gt;&lt;/p&gt;
&lt;p style="FONT-FAMILY: times;"&gt;&lt;font size="2"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;The Credit Facility requires the Company to comply with certain financial covenants, including, maximum capital expenditures, maximum consolidated leverage ratios, minimum consolidated interest coverage ratios and minimum consolidated EBITDA amounts. As of June&amp;#160;30, 2013, the Company was in compliance with the required covenants.&lt;/font&gt;&lt;/p&gt;
&lt;/div&gt;</NonNumbericText><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>nonnum:textBlockItemType</ElementDataType><SimpleDataType>na</SimpleDataType><ElementDefenition>The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.</ElementDefenition><ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 505

 -SubTopic 10

 -Section 50

 -Paragraph 3

 -URI http://asc.fasb.org/extlink&amp;oid=6928386&amp;loc=d3e21475-112644



Reference 2: http://www.xbrl.org/2003/role/presentationRef

 -Publisher SEC

 -Name Regulation S-X (SX)

 -Number 210

 -Section 02

 -Paragraph 19, 20, 22

 -Article 5



Reference 3: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Statement of Financial Accounting Standard (FAS)

 -Number 129

 -Paragraph 2, 4

 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 4: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 210

 -SubTopic 10

 -Section S99

 -Paragraph 1

 -Subparagraph (SX 210.5-02.19,20,22)

 -URI http://asc.fasb.org/extlink&amp;oid=6877327&amp;loc=d3e13212-122682



</ElementReferences><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>LONG-TERM DEBT</Label></Row></Rows><Footnotes /><IsEquityReport>false</IsEquityReport><ReportName>LONG-TERM DEBT</ReportName><MonetaryRoundingLevel>UnKnown</MonetaryRoundingLevel><SharesRoundingLevel>UnKnown</SharesRoundingLevel><PerShareRoundingLevel>UnKnown</PerShareRoundingLevel><ExchangeRateRoundingLevel>UnKnown</ExchangeRateRoundingLevel><HasCustomUnits>true</HasCustomUnits><IsEmbedReport>false</IsEmbedReport><IsMultiCurrency>false</IsMultiCurrency><ReportType>Sheet</ReportType><RoleURI>http://www.mtrgaming.com/role/DisclosureLongTermDebt</RoleURI><NumberOfCols>1</NumberOfCols><NumberOfRows>2</NumberOfRows></InstanceReport>
