Primary aortic tumours are very rare. To our knowledge, only 120 cases had been reported in the world literature. Their clinical presentation is not specific. They are usually diagnosed at aortic surgery or by post-mortem examination. Intimal sarcoma is the most frequent histological type. We report a case of intimal sarcoma of the thoracic aorta diagnosed on autopsy of a 48-year-old man victim of sudden death. The main problem raised by intimal sarcoma lies in its poor differentiation or lack of differentiation. Thus, the pathologist must perform a phenotypic analysis as complete as possible of this tumor.