SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): March 17, 2011

PRIMUS TELECOMMUNICATIONS GROUP, INCORPORATED

(Exact name of registrant as specified in its charter)

7901 Jones Branch Drive, Suite 900, McLean, VA 22102

(Address of principal executive offices and zip code)

Registrant’s telephone number, including area code: (703) 902-2800

Not applicable

(Former name or former address, if changed since last report.)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

On March 17, 2011, Primus Telecommunications Group, Incorporated (“we” or us”) issued a press release announcing our financial results for the quarter ended December 31, 2010. The text of the press release is included as an exhibit to this Form 8-K. Pursuant to the rules and regulations of the Securities and Exchange Commission (the “Commission”), such exhibit and the information set forth therein and herein are deemed to be furnished to, and shall not be deemed to be filed with or incorporated by reference into any filing with the Commission.

Non-GAAP Measures

Our press release and financial tables include the following non-GAAP financial information:

Adjusted EBITDA

Adjusted EBITDA, as defined by us, consists of net income (loss) before reorganization items, net, share-based compensation expense, depreciation and amortization, asset impairment expense, gain (loss) on sale or disposal of assets, interest expense, amortization or accretion on debt discount or premium, gain (loss) on early extinguishment or restructuring of debt, interest income and other income (expense), gain (loss) from contingent value rights valuation, foreign currency transaction gain (loss), income tax benefit (expense), income (expense) attributable to the non-controlling interest, income (loss) from discontinued operations, net of tax, and income (loss) from sale of discontinued operations, net of tax. Our definition of Adjusted EBITDA may not be similar to Adjusted EBITDA measures presented by other companies, is not a measurement under generally accepted accounting principles in the United States, and should be considered in addition to, but not as a substitute for, the information contained in our statements of operations.

We believe Adjusted EBITDA is an important performance measurement for our investors because it gives them a metric to analyze our results exclusive of certain non-cash items and items which do not directly correlate to our business of selling and provisioning telecommunications services. We believe Adjusted EBITDA provides further insight into our current performance and period to period performance on a qualitative basis and is a measure that we use to evaluate our results and performance of our management team.

Free Cash Flow

Free Cash Flow, as defined by us, consists of net cash provided by (used in) operating activities before reorganization items less net cash used in the purchase of property and equipment. Free Cash Flow, as defined above, may not be similar to Free Cash Flow measures presented by other companies, is not a measurement under generally accepted accounting principles in the United States, and should be considered in addition to, but not as a substitute for, the information contained in our consolidated statements of cash flows.

We believe Free Cash Flow provides a measure of our ability, after making our capital expenditures and other investments in our infrastructure, to meet scheduled debt payments. We use Free Cash Flow to monitor the impact of our operations on our cash reserves and our ability to generate sufficient cash flow to fund our scheduled debt maturities and other financing activities, including discretionary refinancings and retirements of debt. Because Free Cash Flow represents the amount of cash generated or used in operating activities and used in the purchase of property and equipment before deductions for scheduled

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debt maturities and other fixed obligations (such as capital leases, vendor financing and other long-term obligations), you should not use it as a measure of the amount of cash available for discretionary expenditures.

(a) and (b) Not applicable.

(c) Exhibits.

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SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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EXHIBIT INDEX

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