We performed a prospective study of the results of treatment of primary cutaneous melanoma of the foot in 282 patients to determine if there were any factors that could predict survival. These patients were part of a group of 1018 patients who had primary cutaneous melanoma affecting the lower extremity. We found that 184 (65 per cent) of the 282 patients had a tumor that extended into the reticular dermis or subcutaneous tissue (a Level-IV or V lesion according to the system of Clark et al.). Sixty-three patients (22 per cent) had evidence of local, regional, or distant metastatic disease at the time of presentation. Location of the melanoma on the plantar aspect of the foot was found to be an independent variable that was associated with a poorer rate of survival (56 per cent at five years and 46 per cent at ten years) compared with a dorsally located melanoma (80 per cent at five years and 67 per cent at ten years). Subungual lesions were associated with an extremely low rate of survival (17 per cent at ten years); however, because of the small number of subungual lesions that were followed, the difference in survival between the patients who had a plantar lesion and those who had a subungual lesion was not significant (p = 0.52). Variables, in order of decreasing importance, that had independent prognostic significance for survival of patients who had a melanoma of the foot were the clinical stage of the lesion at the time of presentation (p < 0.001) and the age of the patient (p < 0.03), as determined by multivariate analysis.(ABSTRACT TRUNCATED AT 250 WORDS)