A 63-year-old man presented to our hospital suffering from dull pain in his right flank and general malaise.Abdominal computed tomography (CT) revealed a 21X14 cm retroperitoneal tumor adjacent to the right kidney. He underwent extirpation of the tumor,which weighed 2,900 g. Histopathological diagnosis was high-grade myxofibrosarcoma. Six months after initial surgery,CT revealed isolated metastasis in the upper lobe of the left lung,which was surgically treated. Eleven months after the original tumor excision, CT revealed lymph node metastasis dorsal to the inferior vena cava,which was also removed. Because he refused to receive adjuvant chemotherapy,he was observed for 2 months until CT revealed multiple liver metastases and para-aortic lymph node metastasis. He underwent 1 cycle of combined chemotherapy with doxorubicin and carboplatin,but metastatic lesions grew larger rapidly and his general state became too poor to continue chemotherapy. He is under best supportive care 17 months after the initial surgery.