A retrospective study of 166 patients with metastatic melanoma of unknown primary was performed. These were selected from 3805 cases of melanoma in Memorial Sloan-Kettering Cancer Center from 1949 through 1975 (an incidence of 4.4%). There were 109 male and 57 female patients, 75 with Stage II disease and 91 with Stage III. The site of predominant involvement in Stage II patients was the axilla (47%). Five- and ten year survival rates of Stage II patients were 46% and 41%, respectively. The only factor that was shown to influence their survival was the delay (three months or more) of radical lymphadenectomy after initial histologic diagnosis. As expected, the prognosis of Stage III patients was very poor. Our study showed that patients with metastatic melanoma of unknown primary followed a similar clinical course as the Stages II and III patients with overt primary lesion. Stage II patients could expect a reasonable survival, the treatment of choice being prompt radical regional lymphadenectomy.