Background: Mohs micrographic surgery is thought to be a useful therapy for cutaneous melanoma. Controversy persists, however, because there are few published reports that document its safety and efficacy. Objective: Our purpose was to determine the safety and efficacy of Mohs micrographic surgery for the treatment of cutaneous melanoma. Methods: A consecutive sample of 535 patients referred for treatment of 553 primary cutaneous melanomas was entered into the study. Of this sample, 99.5% of patients completed their first 5 years of follow-up. All melanomas were excised by means of fresh-tissue Mohs micrographic surgery with frozen-section examination of the margin. The 5-year Kaplan-Meier melanoma mortality, metastasis, and local recurrence rates were compared with historical control cases. Results: Mohs micrographic surgery provided 5-year survival and metastatic rates equivalent to or better than historical controls that were treated by standard wide-margin surgery. Satellite metastases were not more common with the narrow margins used with Mohs micrographic surgery. Local recurrences from inadequate excision of the primary tumor were infrequent (0.5%). The majority of melanomas were successfully excised with a narrow margin (83% were excised with a 6 mm margin). Conclusion: Mohs micrographic surgery is an effective therapy for primary cutaneous melanoma. It may be particularly useful to conserve tissue for melanomas on the head, neck, hands, or feet or for melanomas with indistinct clinical margins. (J Am Acad Dermatol 1997;37:236-45.)