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

DATE OF REPORT (Date of earliest event reported) January 31, 2013

TELLABS, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (630) 798-8800

N/A

(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 January 31, 2013, Tellabs, Inc. is reporting its results of operations for its fiscal fourth quarter ended December 28, 2012. A copy of the press release issued by Tellabs, Inc. concerning the foregoing results is furnished herewith as Exhibit 99.1.

The information contained in this Item 2.02 and related information in the accompanying Exhibit 99.1 shall not be incorporated by reference into any filing of Tellabs, Inc., whether made before or after the date hereof, regardless of any general incorporation language in such filing, unless expressly incorporated by specific reference to such filing. The information in this Item 2.02, including related information in Exhibit 99.1 hereto, shall not be deemed to be “filed” for 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.

In addition to reporting financial results in accordance with U.S. generally accepted accounting principles (GAAP), Tellabs, Inc. has provided non-GAAP financial measures in the press release attached as Exhibit 99.1 as additional information to evaluate our operating performance. These operating performance measures have not been prepared in accordance with GAAP and may be different from measures used by other companies. Whenever we use non-GAAP financial performance measures, we provide a reconciliation of non-GAAP financial performance measures to the most closely applicable GAAP financial performance measure. Management believes the non-GAAP financial performance measures are an important measure of operating performance and provides useful information to investors to better evaluate the operating performance of our business as it highlights trends in our business that may not otherwise be apparent when relying solely on GAAP measures and because it facilitates comparisons to historical results of operations. Management uses these non-GAAP financial performance measures as supplements to our GAAP results in order to provide a more complete understanding of the factors and trends affecting our business as well as for business planning and performance management. Management discloses this information publicly along with a reconciliation of the comparable GAAP amounts, to provide access to the detail and general nature of adjustments made to GAAP financial results. While some of these excluded items have been periodically reported in our statements of operations, including significant restructuring and other charges, their occurrence in future periods depends on future business and economic factors, among other evaluation criteria, and the occurrence of such events and factors may frequently be beyond the control of management.

Item 2.05 Costs Associated with Exit or Disposal Activities

On January 31, 2013, management initiated a restructuring plan that is designed to align expenses with revenue. Tellabs is discontinuing the 9200 product and reducing operating expenses. Actions under this plan are expected to be substantially completed by the end of the second quarter of 2013. We expect to record pretax charges of approximately $38 million, primarily in the first quarter of 2013. The pretax charges will consist of $18 million for workforce reductions of approximately 300 employees, $16 million for facility- and asset-related charges, and $4 million for software and other contract cancellations. Estimated cash payments under this plan are expected to be $25 million beginning in the first quarter of 2013 and continuing through the end of 2017.

This Current Report on Form 8-K contains forward-looking statements, including, but not limited to, statements regarding the expected charges and costs related to the above-described restructuring plan. These forward looking statements are only predictions based on current information and expectations and are subject to certain risks and uncertainties. Factors that might cause such a difference include, but are not limited to, risks associated with: possible changes in the amount and nature of the expected costs and charges, the competitive landscape, including pricing and margin pressures, the response of customers and competitors to changes in our business, industry consolidation, the introduction of new products, the entrance into new markets, the ability to secure necessary resources, the ability to realize anticipated savings under our cost-reduction initiatives, and overall negative economic conditions generally and disruptions in credit, capital markets and fluctuations in currencies, including specific impacts of these conditions on the telecommunications industry and other factors as more fully described in our Annual Report on Form 10-K for the fiscal year ended December 30, 2011, supplemented or modified in subsequent filings with the SEC, under the caption “Risk Factors.” In light of these factors investors are advised not to rely on forward-looking statements in deciding whether to buy, sell or hold the company’s securities. The company undertakes no obligation to revise or update these forward –looking statements to reflect events or circumstances after today or to reflect the occurrence of unanticipated events.

Item 9.01 Financial Statements and Exhibits

(d) Exhibits.

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 thereunto duly authorized.

January 31, 2013

(Date)

EXHIBIT INDEX