Aortoenteric fistula is a rare but deadly medical emergency. Primary fistulas occur between the native aorta and the intestinal tract. Secondary fistulas occur between an aortic graft and the gastrointestinal tract. Patients often present with a "herald bleed," followed by massive gastrointestinal hemorrhage. Sepsis and abdominal pain in a patient who has had an aortic graft may also indicate the formation of a fistula. Prompt intervention is imperative; the mortality rate is 100 percent if the condition is left untreated. In clinically stable patients with a herald bleed, evaluation usually consists of endoscopy in an operating room. Computed tomographic scanning is useful for patients with signs of sepsis; scans showing an aortic graft surrounded by inflammation and abscess formation may indicate fistula formation. Clinically unstable patients require immediate laparotomy. Even in surgically treated patients, the mortality rate is approximately 60 percent.