Aortoenteric fistula (AEF) is an uncommon complication of abdominal aorta aneurysms. They are divided into two types: primary AEF due to a spontaneous communication of the lumen of an aortic aneurysm and an intestinal loop, usually the duodenum, and secondary AEF, which are more common and occur in patients who have undergone surgical repair of aneurysms with prosthetic implants. The most frequent presenting sign of AEF is upper gastrointestinal bleeding. Clinical suspicion is essential in the diagnostic approach to AEF and the most commonly used techniques for its diagnosis are endoscopy and computed tomography (CT). However, it is not unusual for the results of these techniques to be negative and for the diagnosis to be made at surgery. We present three cases of AEF (one primary) with distinct patterns of upper gastrointestinal bleeding, in which preoperative diagnosis was allowed by clinical and helical CT findings. We discuss the role of this technique in the diagnosis of this entity and describe the findings that allow AEF to be suspected or confirmed.