Diagnosis of primary tumors of the aorta is difficult. A patient who had a primary intimal sarcoma of the aorta with metastasis presented with obstructive symptoms and computed tomography showed a thrombus-like mass in the aorta. However, transesophageal echocardiography revealed an inhomogeneous and echo-dense mass with an outer membrane, unlike a thrombus, and suggestive of a primary aortic tumor. Pathologic examination of specimens from exploration and autopsy revealed a primary intimal sarcoma. (Circ J 2002; 66: 111 - 113)