This clinical and histologic study of 122 macular melanocytic lesions on the soles of the feet of Japanese subjects revealed ten in situ malignant melanomas. Clinically, the lesions were broad pigmented macules or patches with asymmetric, angular, irregular shapes, and notched borders. The lesions appeared brownish black, and most were variegated from tan to black. The largest diameters were greater than or equal to 9 mm. The demargination of most lesions was not even; that is, one part of the lesion border was vague while another part was sharp. Histologically, an increased number of atypical melanocytes, mainly arranged as solitary units, were observed within the epidermis. Intraepidermal nests of melanocytes were found in five cases. The great majority of malignant melanomas in non-Caucasians affect acral regions--especially the sole of the foot--so, to improve their prognosis, the characteristics of malignant melanoma in situ on the sole must be elucidated.