Aorto-enteric fistulae are either primary or spontaneous, resulting from aneurysms of the aorta, or secondary to aortic surgery. Four symptoms are common to these two types, but every patient known to have an aortic aneurysm or a history of aortic graft surgery who presents with gastrointestinal bleeding or unexplained infection must be regarded as having an aorto-enteric fistula until proved otherwise. The fistula may be detected by duodenoscopy, but it is most often diagnosed at laparotomy, which is indicated when all paraclinical investigations are negative. While primary aorto-enteric fistulae can be treated by insertion of a prosthesis into the aortic aneurysm, secondary fistulae frequently require " extraanatomical " bypasses. In view of the poor prognosis of secondary aorto-enteric fistulae, prophylactic measures in aortic surgery are of paramount importance.