Primary aortoenteric fistulas (PAEF) are rare entities associated with a high mortality. Although several causes have been reported, their occurrence is usually due to erosion of an abdominal aortic aneurysm into the intestinal tract. The most common sites for the fistula are the third and fourth portions of duodenum. The classical triad of gastrointestinal hemorrhage, abdominal mass and abdominal or back pain, though highly suggestive for PAEF, is uncommon. The typical bleeding pattern associated with PAEF is characteristically intermittent, starting with a brief “herald bleeding” followed eventually by major gastrointestinal hemorrhage, often with fatal outcome. The pre-operative examinations are often not helpful and can lead to delayed diagnosis and surgery. In a patient with risk factors for atherosclerosis and significant upper gastrointestinal bleeding in the absence of an evident source, PAEF should be suspected. A high index of suspicion of this condition allows correct diagnosis and definitive treatment to be carried out. If PAEF is suspected and the patient is unstable the surgeon should be prepared to skip the preoperative investigations in favour of early surgical exploration. Definitive treatment includes primary duodenal repair and aortic aneurismal resection with graft “in situ” replacement. The authors present a successfully treated case and stress the importance of clinical suspicion in order to achieve correct diagnosis and treatment.