UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

December 1, 2011

Date of Report (Date of earliest event reported)

SYCAMORE NETWORKS, INC.

(Exact name of registrant as specified in its charter)

220 Mill Road

Chelmsford, MA 01824

(Address of principal executive offices)

(Zip code)

Registrant’s telephone number, including area code: (978) 250-2900

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:

Item 2.02: Results of Operations and Financial Condition.

On December 1, 2011, the Registrant reported its financial results for the first quarter ended October 29, 2011.

A copy of the press release issued by the Registrant with respect to the foregoing is attached as Exhibit 99.1 to this Current Report on Form 8-K and incorporated by reference herein.

The Registrant provides non-GAAP financial data in addition to providing financial results in accordance with generally accepted accounting principles (“GAAP”). These measures are not in accordance with or an alternative for GAAP, and may be different from non-GAAP measures used by other companies. The reconciliation between the GAAP basis and the non-GAAP basis financial data is provided in a table immediately following the Unaudited Consolidated Statements of Operations included with Exhibit 99.1. The Registrant believes that the items excluded from the non-GAAP results have one or more of the following characteristics: their magnitude and timing are largely outside of the Registrant’s control; they are unrelated to the ongoing operation of the business in the ordinary course; they are unusual, and the Registrant does not expect them to occur in the ordinary course of business; or they are non-operational, non-cash expenses involving equity grants.

The non-GAAP financial data is provided to enhance the reader’s overall understanding of the Registrant’s current financial performance and its prospects for the future. Specifically, the Registrant believes the non-GAAP results provide useful information to both management and investors by excluding certain expense and income items that the Registrant believes are not indicative of the Registrant’s core operating results. In addition, since the Registrant has historically reported non-GAAP results to the investment community, the Registrant believes the inclusion of non-GAAP numbers provides consistency in its financial reporting. Further, these non-GAAP results are one of the primary indicators management uses for planning and forecasting in future periods. The non-GAAP financial data should be considered in addition to, not as a substitute for or a more appropriate indicator of, operating results, cash flows, or other measures of financial performance prepared in accordance with GAAP.

The information contained herein and in the accompanying Exhibit 99.1 shall not be incorporated by reference into any filing of the Registrant, whether made before or after the date hereof, regardless of any general incorporation language in such filing, unless expressly incorporated by specific reference into such filing. The information in this report, including Exhibit 99.1 hereto, shall not be deemed to be “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended.

Item 9.01: Financial Statements and Exhibits.

(d) Exhibits

SIGNATURES

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 thereunto duly authorized.

Dated: December 1, 2011