Primary malignant tumors of the aorta are extremely rare. The case of a 64-year-old woman who presented with peripheral embolism to both femoropopliteal arteries is reported. The search for a source revealed a polypoid lesion severely narrowing the lumen of the distal thoracic aorta. Differential diagnosis included thrombus and primary aortic tumor. Extirpation of the tumorous lesion was performed. Histologic examination revealed intimal aortic sarcoma of endothelial cell origin. Although the liver was the only site of suspected metastases at the time of operation, during the 18-month follow-up until the patient's death, generalized metastatic spread had developed. This case report thus demonstrates the generally poor prognosis of this rare variety of aortic sarcoma, in particular when symptoms have already occurred.