Background. Gastrointestinal bleeding of non-ulcerative etiology remains an urgent problem of modern medicine. An aorto-intestinal fistula caused by an aortic aneurysm is one of the rarest causes of intestinal bleeding. Objective. To study the incidence of an aortic aneurysm with a complicated course according to autopsy data and to present a description of a rare case of an aortic aneurysm complicated by the formation of a duodenum fistula, profuse intestinal bleeding with a fatal outcome. Material and methods. The object of the study was the protocols of 2050 autopsies performed in Grodno over 2021-2022, among which in 40 (1.95%) cases the presence of an aortic aneurysm was established. In one case an abdominal aortic aneurysm was complicated by the formation of a fistula with the duodenum and profuse intestinal bleeding which became the direct cause of death. Results. The abdominal aorta was found to be involved in the pathological process in 32 (80.0%) dissections. Along with complications typical for an abdominal aortic aneurysm (bleeding into the retroperitoneal space and abdominal cavity) in 1 (3.1%) of 32 autopsies there has been revealed a formed anastomosis between the aorta and the duodenal lumen which was the cause of intestinal bleeding with fatal outcome. The clinical manifestations of the disease caused difficulties in interpreting the causes of intestinal bleeding. As a result, the fatal complication of an aortic aneurysm was recognized only on the 27th day after hospitalization, 1.5 hours before the patient’s death. Conclusions. The presented clinical case confirms that timely diagnosis of abdominal aortic aneurysms complicated by the formation of fistulas with the intestine is a rare diagnostic challenge. A particular feature of such complications is the fact that patients who are initially in a very serious condition are out of sight of vascular surgeons which leads to a delay in the provision of timely specialized care.