[A case of malignant melanoma that metastasized to the liver]. We report a rare case of malignant melanoma that metastasized to the liver. A 36-year-old male underwent radical mastectomy for malignant melanoma of the left breast 5 months before he was admitted to the Chugoku Rosai Hospital. He was diagnosed with advanced liver metastasis by liver biopsy. Because the patient showed no deterioration of his liver function, he was treated by a combination chemotherapy including dacarbazine and fotemustine. The patient responded to the chemotherapy, and there were no abnormalities in the physical examinations and blood chemistry. A computed tomography showed the disappearance of the hepatic tumor in 11 months after the initiation of the chemotherapy. The results of the histological diagnosis were as follows: high-grade spindle cell malignant melanoma, positive for S-100 protein. A small round cell component was found in some areas. The clinical course, histological findings and the results of immunohistochemical staining suggested the metastatic nature of the tumor. Immunohistochemical studies revealed that the small round cell component had epithelial antigens and was of epithelial origin. This case was of the "collision tumor" type. The round cell component was not a carcinoma, but a metastatic melanoma. The round cell component could be differentiated from a metastatic carcinoma by the expression of epithelial antigens, the distribution of the lesions and the patient's clinical course. We therefore concluded that our case was a rare, but not exceptional case of melanoma with metastasis to the liver, in which epithelial antigens were expressed.