- Primary aortoenteric fistula is a rare but catastrophic cause of gastrointestinal bleeding. The diagnosis of primary aortoenteric fistula is difficult to make and is usually accompanied by a very high level of clinical suspicion. It should be considered in any elderly patient presenting with upper gastrointestinal bleeding in the context of a known abdominal aortic aneurysm. Prompt surgical intervention is necessary. We present the case of a 78-year-old man with a history of atherosclerotic abdominal aortic aneurysm which is presented with massive upper gastrointestinal bleeding due to a primary aortoduodenal fistula. Initial misdiagnosis led to a delay in treatment and the patient succumbed to the illness.