The incidence of malignant oral melanoma amounts to more than 10% of all malignant melanomas in Japan, which is higher than that reported by Conley and Park. This paper describes a case of malignant melanoma of the left mandible that resulted in disseminated metastases.A 31-year-old man presented at Nagoya University Hospital. First examination in Apr, 1977 revealed diffuse swelling and pigmentation of the left mandibular gingiva with ulceration of 5mm in diameter. The roentgenographic findings showed diffuse bone resorption in the left premolar and molar regions, presenting a pattern of horizontal bone resorption seen in periodontal diseases.Excision of the tumor was performed with partial dissection of the right neck and total dissection of the left neck. This surgical intervention was followed by chemotherapy with 5-Fu, MMC and EX. Histopathologically the tumor was localized at the primary site without other tumor lesion in regional lymphnodes (pT4pN0pM0, stage 1b).In Apr, 1978 skin metastasis was found. It soon began to develop into multilesional, extensive subcutaneous metastases. The metastatic lesions responded completely to immunotherapy with local BCG. However, the administration of BCG by multiple puncture tine technics produced no effect.From Nov, 1978 when lung metastasis was detected until Feb, 1980 when brain metastasis was detected, immunotherapy failed to produce any remarkable change in the metastatic tumors. By chemotherapy consisting of 12 courses of DTIC, Me-CCNU and hydroxyurea over 15 months, partial response such as reduction of the tumor size and depigmentation was obtained at each course. However, any tumor disappeared. By the end of this period, despite increase in the number and size of the metastatic tumors, the behavior of the malignant melanoma was subdued.In Feb, 1980 he complained of headache and brain metastasis was detected by CT-scan. In spite of ACNU and THFT therapy, the patient died with complications of DIC and DM on May 26, 1980, 3 years and a month after his first visit.