Seven cases of rupture of an abdominal aortic aneurysm into the inferior vena cava are reported. In the management of this rare condition it is important to make the diagnosis preoperatively. Most cases show evidence of a large arteriovenous fistula which can, on occasions, dominate the clinical picture, e.g. cyanosed lower extremities or cardiac failure, but abdominal pain is the major feature. Careful examination of all patients with a ruptured aneurysm, particularly listening for an abdominal bruit, will usually allow the diagnosis of aortocaval rupture to be made.