A review of the literature on melanoma indicates that age, sex, size, ulceration, presence of satellites, absence of melanin, and whether or not the tumor is markedly raised above the surface of the surrounding skin are all useful criteria in evaluating the prognosis in Stage I cutaneous melanoma. Histological factors include the tumor type, the mitotic rate, and the maximum thickness of the tumor. The last is accurate for prognosis--objective, reproducible, and directly proportional to the mortality rate. Tumors less than 0.76 mm thick rarely, if ever, metastasize--and it appears that the size of the resection margin can safely be reduced for such thin tumors. The level of invasion (Clark) is less accurate in predicting the mortality.