The incidence of malignant melanoma is much lower in the Japanese than in caucasians. However, amongst the various types of malignant melanoma, the subungual and periungual sites are commonly found in the Japanese. One hundred and fifty-one cases of cutaneous malignant melanoma were seen over a 25-year period at our hospital. We found that, in 34 patients (23%), the subungual region was involved, a high frequency for one institution. We have analysed these patients and looked at their treatment. The finger nails were affected in 21 cases (62%) and the toe nails in 13 cases (38%). The thumb nails or great toe nails were affected in 25 of the 34 patients (73%). In 25 patients, histopathological features of acral lentiginous melanoma were found, with four cases of superficial spreading melanoma and five of nodular amelanotic melanoma. Of the latter group, four mimicked fibrous histiocytic tumour, and one was a desmoplastic malignant melanoma. The proportion of patients presenting with stage III disease decreased after 1982, with a corresponding increase in patients whose tumour thickness was less than 4 mm (stage II). Concurrently, the prognosis for subungual malignant melanoma improved. The 5-year survival rate in each of the periods 1969-82 and 1983-93 was 53 and 87%, respectively. This is similar to that found in plantar malignant melanoma and is felt to be due to a greater public awareness of the condition and to the introduction of effective chemotherapy (the DTIC-AC nitrosurea-vincristine (DAV) regimen). Although the frequency of malignant melanoma is rather low in the Japanese, our data indicate that there is a high incidence of subungual malignant melanoma. Public awareness of the early stage of malignant melanoma seems to have improved prognosis.