We report a primary malignant tumor of the thoracic aorta with clinical-course from onset to death. A 63-year-old male was admitted to our hospital with intermittent claudication and bilateral lower extremity pain. The diagnosis was established after an abdominal operation. The tumor was subsequently resected including the thoracic aorta and replaced with a dacron graft. The pathological finding was of a primary intimal sarcoma. The patient lived for more than two years excluding the hospitalized period after the diagnosis.