The records of sixty patients who had a malignant melanoma of the foot or ankle were reviewed retrospectively to determine the clinical features, prognostic factors, and distinguishing characteristics. Fifty-seven patients were white and three were black. There were forty-two women and eighteen men (a female-to-male ratio of 2.3 to 1). The mean age at the time of presentation was fifty-seven years (range, twenty-two to eighty-three years). The most common site of involvement was the plantar aspect of the foot. The mean duration of follow-up was forty-five months (range, three to 144 months). Kaplan-Meier life-table analysis revealed an over-all five-year survival rate of 63 per cent and an over-all ten-year survival rate of 51 per cent. The mean duration of survival for the patients who had a plantar or subungual lesion was significantly shorter than that for the patients who had a lesion at another site on the dorsal aspect of the foot or on the ankle (forty-seven compared with seventy-two months) (p = 0.02). The mean depth of the lesion, according to the criteria of Breslow, was 3.03 millimeters, and the mean level, according to the classification of Clark et al., was IV. According to the classification of the American Joint Commission on Cancer, forty-three patients had stage-I or II (local) disease, thirteen had stage-III disease (nodal or in-transit disease, defined as cutaneous or subcutaneous metastases more than two centimeters from the primary tumor but not beyond the regional lymph nodes), and four had stage-IV disease (distant visceral metastases) at the time of presentation. Lesions at plantar and subungual sites were also associated with a higher prevalence of clinical misdiagnosis compared with lesions on the dorsal aspect of the foot or on the ankle (p = 0.02). The misdiagnoses included a benign nevus (one patient), a paronychia (one patient), a pyogenic granuloma (two patients), a plantar wart (three patients), a ganglion cyst (one patient), a blister (two patients), and a traumatic lesion (five patients).(ABSTRACT TRUNCATED AT 250 WORDS)