Exhibit 5.1


                                   May 1, 2002

Mentor Graphics Corporation
8005 SW Boeckman Road
Wilsonville, Oregon  97070-7777

Ladies and Gentlemen:

        I have acted as counsel for Mentor Graphics Corporation, an Oregon
corporation (the "Company"), in connection with the filing of a Registration
Statement on Form S-8 (the "Registration Statement") under the Securities Act of
1933, as amended, covering the issuance by the Company of 1,190,848 shares of
Common Stock, no par value (the "Shares"), of the Company. Pursuant to the
Agreement and Plan of Merger and Reorganization dated as of March 12, 2002, by
and among the Company, Fresno Corporation("Fresno"), a Delaware corporation and
wholly-owned subsidiary of the Company, and IKOS Systems, Inc., a Delaware
corporation ("IKOS"), the Company assumed all outstanding options to purchase
common stock of IKOS (the "Options") under the Virtual Machine Works, Inc. 1994
Incentive Stock Option Plan, the IKOS Systems, Inc. 1995 Stock Option Plan, the
IKOS Systems, Inc. 1995 Outside Directors Stock Option Plan, and the IKOS
Systems, Inc. 2000 Nonstatutory Stock Option Plan (collectively, the "Plans"),
and, upon the consummation of the merger of Fresno into IKOS by filing a
certificate of merger with the Secretary of State of Delaware on April 17, 2002,
the Options became exercisable to purchase Shares. I have reviewed the corporate
actions of the Company in connection with this matter and have examined those
documents, corporate records, and other instruments I deemed necessary for the
purposes of this opinion.

        Based on the foregoing, it is my opinion that:

        1. The Company is a corporation duly organized and validly existing
under the laws of the State of Oregon.

        2. The issuance of the Shares has been duly authorized and, when issued
and sold in accordance with the terms of the Plans, will be legally issued,
fully paid and nonassessable.

        I hereby consent to the filing of this opinion as an exhibit to the
Registration Statement.


                                            Very truly yours,

                                            /s/ Dean M. Freed

                                            Dean M. Freed
                                            Vice President and General Counsel