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, 2011

or

For the transition period from             to             .

Commission file number 1-12043

OPPENHEIMER HOLDINGS INC.

(Exact name of registrant as specified in its charter)

Registrant’s Telephone number, including area code: (212) 668-8000

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

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

Title of class

Not Applicable

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.

Yes   ¨    No  x

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act.     Yes   ¨    No  x

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 whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (Section 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). 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.  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting company. See definition of “large accelerated filer”, “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). Yes     ¨ No     x

The aggregate market value of the voting stock of the Company held by non-affiliates of the Company cannot be calculated in a meaningful way because there is only limited trading in the class of voting stock of the Company. The aggregate market value of the Class A non-voting common stock held by non-affiliates of the Company at June 30, 2011 was $382.8 million based on the per share closing price of the Class A non-voting common stock on the New York Stock Exchange as at June 30, 2011 of $28.21.

The number of shares of the Company’s Class A non-voting common stock and Class B voting common stock (being the only classes of common stock of the Company) outstanding on February 28, 2012 was 13,589,062 and 99,680 shares, respectively.

DOCUMENTS INCORPORATED BY REFERENCE

The Company’s definitive Proxy Statement for the 2012 Annual Meeting of Stockholders to be filed by the Company pursuant to Regulation 14A is incorporated into Items 10, 11, 12, 13 and 14 of Part III of this Form 10-K.

EXPLANATORY NOTE

The Company is amending its Annual Report on Form 10-K for the year ended December 31, 2011 to add Exhibit 10.29 to its Exhibit Index consisting of its lease for the premises at 85 Broad Street, New York, NY, a copy of which was previously filed with its Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2011.

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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 amendment to report to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of New York, State of New York, on the 27th day of March, 2012.

OPPENHEIMER HOLDINGS INC.

BY: /s/ E.K. Roberts

E.K. Roberts, President

(on behalf of the Registrant)

Pursuant to the requirements of the Securities Exchange Act of 1934, this amendment to 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

The Exhibits listed below have been heretofore filed by the Company pursuant to Section 13 or 15(d) of the Exchange Act and are hereby incorporated herein by reference to the pertinent prior filing indicated.

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