Diffuse Cutaneous Melanosis is a rare clinical condition characterized by rapidly acquired skin pigmentation that can occur in the course of advanced metastatic melanoma. A 59 year old patient with malign melanoma who developed diffuse cutaneous melanosis in the course of the disease is presented. He had multiple hepatic metastasis, lung metastasis, and multiple bone metastases. After the initiation of chemotherapy, he developed progressively darkening of the entire skin, darkened urine. Four months after the onset of melanosis, the patient died. The prognosis are poor in patients with diffuse cutaneous melanosis associated with malign melanoma.