EXHIBIT 5.1 [LETTERHEAD OF IRELL & MANELLA LLP] April 16, 1999 Mattel, Inc. 333 Continental Boulevard El Segundo, California 90245-5012 Re: Series D Medium-Term Notes -------------------------- Ladies and Gentlemen: We have acted as counsel for Mattel, Inc., a Delaware corporation (the "Company"), in connection with the Company's Registration Statement on Form S-3 (No. 333-68017)(the "Registration Statement"), with respect to the registration under the Securities Act of 1933, as amended (the "Act"), of up to $400,000,000 (or the equivalent thereof in one or more foreign currencies or composite currencies) aggregate initial offering price of an indeterminate amount of various Securities (as defined in the Registration Statement). The Registration Statement was initially filed with the Securities and Exchange Commission (the "Commission") on November 25, 1998, and was declared effective by the Commission on December 8, 1998, having the effect of qualifying the indenture dated as of February 15, 1996 (the "Indenture") between the Company and Chase Manhattan Bank and Trust Company, N.A. (formerly Chemical Trust Company of California), as trustee (the "Trustee"), under the Trust Indenture Act of 1939, as amended (the "Trust Indenture Act"). Pursuant to the Indenture, the Company proposes to issue up to $400,000,000 (or the equivalent thereof in one or more foreign currencies or composite currencies) in aggregate principal amount of Securities designated as Series D Medium-Term Notes (the "Notes"). The Notes will be offered on a continuing basis pursuant to Rule 415 under the Act by the Prospectus dated April 16, 1999 (the "Basic Prospectus"), as supplemented by the Prospectus Supplement dated April 16, 1999 (the "Supplement" and, together with the Basic Prospectus, the "Prospectus"). The Prospectus will be further supplemented by pricing supplements, each of which will be dated approximately as of the date of sale of particular Notes and will furnish information as to the specific terms thereof. For purposes of this opinion, we have reviewed such corporate records, agreements and other instruments, and certificates of public officials, and have considered such questions of law, as we deemed necessary or appropriate for the purposes of this opinion. Mattel, Inc. April 16, 1999 Page 2 On the basis of the foregoing and in reliance thereon, we are of the opinion that the issuance and sale of Notes have been duly authorized and, when the final terms of a particular Note and of its issuance and sale have been duly established in accordance with the provisions of the Indenture and when the Notes have been executed and authenticated in accordance with the provisions of the Indenture and delivered to and paid for by the purchasers thereof in the manner provided in the Distribution Agreement dated April 16, 1999 between the Company and, as Agents, Morgan Stanley & Co. Incorporated and Credit Suisse First Boston Corporation, the Notes will be entitled to the benefits of the Indenture and will be valid and binding obligations of the Company, enforceable in accordance with their respective terms. With respect to the opinions rendered above relating to enforceability of the Notes: (i) such opinions are subject to the following exceptions, limitations and qualifications: (a) the effect of bankruptcy, insolvency and similar laws affecting creditors' rights generally; (b) the effect of general principles of equity, including, without limitation, concepts of materiality, reasonableness, good faith and fair dealing and the possible unavailability of specific performance or injunctive relief, regardless of whether such enforceability is considered in a proceeding in equity or at law; and (c) certain rights, remedies and waivers contained in the Indenture or the Notes may be limited or rendered ineffective by applicable California laws or judicial decisions governing such provisions, but such laws or judicial decisions do not render the Indenture or the Notes invalid or unenforceable as a whole; (ii) we express no opinion with respect to (a) the enforceability of the waiver of rights or defenses contained in Section 4.4 of the Indenture or (b) whether acceleration of any Notes that may have been sold for less than the full face amount thereof may affect the collectibility of that portion of the stated principal amount thereof that might be determined to constitute unearned interest thereon; and (iii) in rendering such opinions, we have assumed that the interest rates on the Notes at the time of their determination will not exceed the maximum rate permitted under the usury laws of the State of California. To the extent the obligations of the Company under the Indenture and with respect to the Notes may be dependent upon such matters, we assume for purposes of the opinions rendered above that the Trustee has complied with any applicable requirement to file returns and pay taxes under the Franchise Tax Law of the State of California; that the Trustee is duly organized, validly existing and in good standing under the laws of its jurisdiction of organization; that the Trustee is duly qualified to engage in the activities contemplated by the Indenture; that the Indenture has been duly authorized, executed and delivered by the Trustee and constitutes the valid and binding obligation of the Trustee enforceable against the Trustee in accordance with its terms; that, with respect to acting as a Mattel, Inc. April 16, 1999 Page 3 trustee under the Indenture, the Trustee is generally in compliance with all applicable laws and regulations; and that the Trustee has the requisite organizational and legal power and authority to perform its obligations under the Indenture. Please be advised that we are licensed to practice law only in the State of California. We express no opinion as to the law of any jurisdiction other than the laws of the State of California, the Delaware General Corporation Law and the United States federal laws. This opinion is being rendered as of the date hereof and we assume no obligations whatsoever to modify or update this opinion subsequent to the date hereof, or to correct this opinion to the extent it may be rendered inaccurate as a result of facts, circumstances or laws not in existence on the date hereof. This opinion is rendered solely for your benefit in connection with the transactions described above. We hereby consent to the use of this opinion as an exhibit to the Company's Current Report on Form 8-K, event date April 16, 1999. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act. Very truly yours, /s/ Irell & Manella LLP Irell & Manella LLP