A very rare case of a myxosarcoma with metastases to the brain is reported. A 33-year-old female was admitted to our hospital because of lassitude, fever, slight left hemiparesis, headache and other signs of intracranial hypertension and cardiac symptoms such as dyspnea and palpitation. She had the cardiac symptoms once 14 years before, which reappeared and rapidly aggravated two months before the admission. Cerebral angiography revealed a mass in the right temporal lobe and physical and laboratory examinations revealed mitral value failure and hyperthyroidism. On the next day, March 19, 1976, a grossly cystic 60 gm tumor was totally removed which was largely imbedded in the subcortex of the right temporal lobe. The symptoms except for the cardiac symptoms and disseminated intravascular coagulopathy rapidly improved, but headache and left hemiparesis returned 13 days postoperatively. She died suddenly 18 days after the operation due to acute cardiac failure. Autopsy revealed two separate hard and solid tumors both attached to the mitral valve and occupied the whole left atrium and another metastasis to the frontal lobe which had not been diagnosed before the death. Microscopic examinations including electronmicroscopic study established the diagnosis of myxosarcoma in all the four tumors.