Fifty-one white Caucasian patients from the west of Scotland, with stage I primary malignant melanoma arising on the plantar surface were studied. Subungual lesions were excluded from the study. Clinical and pathological features were related to survival, and compared with a group of 239 cases of clinical stage 1 melanoma of the lower limb, excluding the foot, collected in the same geographical area over the same period of time (1979-84). The average age of patients with plantar melanoma was 67 years and was significantly older than those with leg melanomas, in whom the mean age was 53 years. Twenty patients with plantar lesions had superficial spreading melanomas, 27 had acral lentiginous melanomas, and four had nodular lesions. The female:male ratio was 3:2 which was significantly different from the 7:1 female:male ratio for leg lesions. Plantar melanomas were more commonly ulcerated (57%) than were melanomas on the leg (29%) [P < 0.001]. There was no significant difference between the mean thickness of melanomas on the plantar surface and those on the leg. Nine (17%) of the patients with plantar melanomas gave a clinical history of pre-existing naevus and in 27% there was pathological evidence of a pre-existing naevus. Disease-free survival at 5 years for the population with plantar melanomas was 82, 51 and 0%, respectively, for melanomas 0-1.49, 1.5-3.49 and over 3.5 mm in thickness. This compares with 95, 71 and 46%, respectively, for leg lesions. In each thickness category patients with leg melanomas have a significantly better survival.(ABSTRACT TRUNCATED AT 250 WORDS)