Diffuse cutaneous melanosis is a rare complication of metastatic melanoma related to a worse prognosis. There are few cases reported in the literature. Its pathogenesis has not been completely elucidated, although studies have suggested certain mechanisms for its occurrence. It is clinically manifested as a blue-gray discoloration of the skin and mucous membranes in a cephalo caudal progression and usually associated with melanuria. Skin and mucosa histopathology reveals only the presence of melanophages in the dermis, mainly perivascular, and free interstitial melanin. We report the case of a 68-year-old male with metastatic melanoma, diffuse hyperpigmentation of the skin and melanuria.