Aorto-caval fistulas are an uncommon complication of infrarenal aortic aneurysms, being found in 0.22% to 6.04% of all cases. Operating on 1231 patients with abdominal aortic aneurysm in the last 30 years we saw 17 patients with an aortocaval fistula. While 5 patients showed an isolated fistula, 12 had an additional rupture of the aneurysm into the retroperitoneal space or the abdominal cavity. Only in four patients was the aorto-caval fistula diagnosed preoperatively. In 16 patients the fistula was closed from within the aorta. One patient needed ligation of the vena cava and the iliac veins. Mortality rate was 40% in the group with isolated fistula and 66.7% in the group with concomitant rupture. Aorto-caval fistula is a severe complication of abdominal aortic aneurysms, which may be fatal and demands early diagnosis and prompt treatment.