A primary aortoenteric fistula (PAEF), defined as a communication between the native aorta and the gastrointestinal tract, is a rare cause of gastrointes-tinal bleeding. The preoperative diagnosis of PAEF is extremely difficult. Consequently, PAEF may cause sudden and unexpected death. We present an autopsy case of a 68-year-old man who died of massive gastro-intestinal bleeding due to a PAEF. Autopsy revealed a pinhole rupture located on the third part of the duode-nal mucosa and fistulized into the adjacent abdominal aortic aneurysrn (AAA). Our case indicates that the aortoenteric fistula can result in fatal gastrointestinal bleeding. Consequently, a PAEF should be included in the differential diagnosis of gastrointestinal bleeding.