Primary aortoduodenal fistula is a serious and rare complication of abdominal aortic aneurysms. This life-threatening disease results most commonly from an abdominal aortic aneurysm, with the fistula forming between the aorta and the third or the fourth portions of the duodenum. Diagnosis is often difficult and urgent adequate surgical treatment as soon as possible is the only therapeutic option to save the lives of these patients. In this paper we report the case of a 76-year-old female admitted to our institution for massive haematemesis, melaena, severe hypotension and violent back pain. The urgent diagnostic work-up revealed an abdominal aortic aneurysm with a strong suspicion of duodenal fistulisation. The diagnosis was confirmed in the operating room, where the patient was immediately submitted to closure of the fistula and in situ aortic reconstruction using an aortic homograft. The postoperative course was uneventful and after 6 months the patient is doing well without any recurrence of infection.