EXHIBIT 5.1

                   [Letterhead of Gibson, Dunn & Crutcher LLP]

                                 March 25, 2002

Cadence Design Systems, Inc.
2655 Seely Avenue, Building 5
San Jose, CA 95134

        Re: Registration Statement on Form S-8 of Cadence Design Systems, Inc.

Ladies and Gentlemen:

        We refer to the registration statement on Form S-8 (the "Registration
Statement"), under the Securities Act of 1933, as amended (the "Securities
Act"), filed by Cadence Design Systems, Inc., a Delaware corporation (the
"Company"), with respect to the proposed offering by the Company of up to
258,843 shares (the "Shares") of its common stock, $0.01 par value per share
(the "Common Stock"), subject to issuance by the Company under its 1998 Stock
Option Plan (the "Plan"). The options issuable under the 1998 Stock Option Plan
were assumed by the Company pursuant to the terms of that certain Agreement and
Plan of Merger, dated as of March 4, 2002, by and among the Company, Jackal
Acquisition, Inc., a California corporation and wholly-owned subsidiary of the
Company, JTA Research Incorporated, a California corporation and Jonathan Yee,
as Shareholder Agent.

        We have examined the originals or certified copies of such corporate
records, certificates of officers of the Company and/or public officials and
such other documents, and have made such other factual and legal investigations
as we deemed relevant and necessary as the basis for the opinions set forth
below. In such examination, we have assumed the genuineness of all signatures,
the authenticity of all documents submitted to us as originals, the conformity
to original documents of all documents submitted to us as conformed or
photostatic copies and the authenticity of the originals of such copies.

        Based on our examination mentioned above, subject to the assumptions
stated above and relying on the statements of fact contained in the documents
that we have examined, we are of the opinion that (i) the issuance by the
Company of the Shares has been duly authorized and (ii) when issued in
accordance with the terms of the Plan, the Shares will be duly and validly
issued, fully paid and non-assessable shares of Common Stock.

        We are admitted to practice in the State of California, and are not
admitted to practice in the State of Delaware. However, for the limited purposes
of our opinions set forth above, we are generally familiar with the General
Corporation Law of the State of Delaware (the "DGCL") as presently in effect and
have made such inquiries as we consider necessary to render this opinion with
respect to a Delaware corporation. This opinion letter is limited to the DGCL,
as it presently exists and to the facts as they presently exist. We express no
opinion with respect to the effect or applicability of the laws of any other
jurisdiction. We assume no obligation to revise or supplement this opinion
letter should the laws of such jurisdictions be changed after the date hereof by
legislative action, judicial decision or otherwise.

        We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement. In giving this consent, we do not admit that we are
within the category of persons whose consent is required under Section 7 of the
Securities Act or the General Rules and Regulations of the Securities and
Exchange Commission.

                                                   Very truly yours,

                                                   GIBSON, DUNN & CRUTCHER LLP