UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K/A

Amendment No. 1

(Mark One)

For the fiscal year ended December 31, 2004

OR

For the transition period from              to              .

Commission File Number: 0-19582

OLD DOMINION FREIGHT LINE, INC.

(Exact name of registrant as specified in its charter)

500 Old Dominion Way

Thomasville, NC 27360

(Address of principal executive offices)

(Zip Code)

(336) 889-5000 (Registrant’s Telephone Number, Including Area Code)

www.odfl.com (Registrant’s Web Site)

Securities registered pursuant to Section 12(b) of the Act: None

Securities registered pursuant to Section 12(g) of the Act:

Common Stock ($0.10 par value)

(Title of class)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of the registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.  x

Indicate by check mark whether the registrant is an accelerated filer (as defined in Exchange Act Rule 12b-2).    Yes  x    No  ¨

The aggregate market value of voting stock held by nonaffiliates of the registrant as of June 30, 2004, was $405,737,249.

As of March 16, 2005, the registrant had 24,845,235 outstanding shares of Common Stock ($0.10 par value).

DOCUMENTS INCORPORATED BY REFERENCE

None.

EXPLANATORY NOTE

This Form 10-K/A (Amendment No. 1) amends the annual report of Old Dominion Freight Line, Inc. on Form 10-K for the year ended December 31, 2004, referred to as the 2004 Form 10-K, filed with the Securities and Exchange Commission (the “SEC”) on March 16, 2005. The purpose of this amendment is to provide a revised independent auditor’s report from Ernst & Young LLP stating that they conducted their audits in accordance with “the standards of the Public Company Accounting Oversight Board (United States)” instead of in accordance with “auditing standards generally accepted in the United States” as originally reported.

This revision had no effect on the Company’s consolidated statements of operations, statements of cash flows or balance sheets.

This Amendment No. 1 is limited in scope to the portion of the 2004 Form 10-K set forth above and does not amend, update or change any other items or disclosures contained in the original 2004 Form 10-K. This Amendment No. 1 continues to speak as of the date of the 2004 Form 10-K, and we have not updated the disclosures in either this Amendment No. 1 or the 2004 Form 10-K to reflect events that occurred subsequent to the filing of the 2004 Form 10-K, other than with respect to the revised independent auditor’s report from Ernst & Young LLP that is included as part of this Amendment No. 1.

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Report of Independent Registered Public Accounting Firm

The Board of Directors and Shareholders

Old Dominion Freight Line, Inc.

We have audited the accompanying consolidated balance sheets of Old Dominion Freight Line, Inc. (the Company) as of December 31, 2004 and 2003 and the related consolidated statements of operations, changes in shareholders’ equity, and cash flows for each of the three years in the period ended December 31, 2004. Our audits also include the financial statement schedule of Old Dominion Freight Line, Inc. listed in Item 15(a). These financial statements and schedule are the responsibility of the Company’s management. Our responsibility is to express an opinion on these financial statements and schedule based on our audits.

We conducted our audits in accordance with the standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements. An audit also includes assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion.

In our opinion, the financial statements referred to above present fairly, in all material respects, the consolidated financial position of Old Dominion Freight Line, Inc. as of December 31, 2004 and 2003, and the consolidated results of its operations and its cash flows for each of the three years in the period ended December 31, 2004, in conformity with U.S. generally accepted accounting principles. Also, in our opinion, the financial statement schedule, when considered in relation to the basic financial statements taken as a whole, presents fairly in all material respects the information set forth therein.

As discussed in Note 1 to the financial statements, effective January 1, 2002, the Company adopted Statement of Financial Accounting Standards No. 142, Goodwill and Other Intangible Assets.

We have also audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States), the effectiveness of the Company’s internal control over financial reporting as of December 31, 2004, based on criteria established in Internal Control – Integrated Framework issued by the Committee of Sponsoring Organizations of the Treadway Commission and our report dated March 14, 2005 expressed an unqualified opinion thereon.

/s/ ERNST & YOUNG LLP

Greensboro, North Carolina

March 14, 2005

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SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Pursuant to the requirements of the Securities Exchange Act of 1934, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated:

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EXHIBIT INDEX

FORM 10-K/A – AMENDMENT NO. 1 TO ANNUAL REPORT ON FORM 10-K

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