Primary aortoenteric fistula is the spontaneous communication between the lumen of the aorta and a portion of the digestive tract. The most common cause is the erosion of an abdominal aortic aneurysm into the 3rd or 4th portion of the duodenum. It manifests clinically as gastrointestinal bleeding, with or without abdominal pain and a pulsatile abdominal mass on physical exam. Gastrointestinal bleeding is initially recurrent and self-limiting and progresses to fatal exsanguinating hemorrhage. Endoscopic examination diagnoses only 25% of aortoenteric fistulas because these are usually located in the distal duodenum. Contrast computed tomography of the abdomen and pelvis is diagnostic in only 60% of cases. We report three cases with this condition. A 67-year-old male presenting with an upper gastrointestinal bleeding. He was operated and a communication between an aortic aneurysm and the duodenum was found and surgically repaired. The patient is well. A 67-year-old male with an abdominal aortic aneurysm presenting with abdominal pain. He was operated and anticoagulated. In the postoperative period he had a massive gastrointestinal bleeding and a new CAT scan revealed an aorto enteric fistula that was surgically repaired. The patient is well. An 82-year-old male with an abdominal aortic aneurysm presenting with hematochezia. A CAT scan revealed a communication between the aneurysm and the third portion of the duodenum, that was surgically repaired. The patient died in the eighth postoperative day.