IN RECENT YEARS several case reports1-4of successful repair of an arteriovenous fistula between an atherosclerotic aneurysm of the abdominal aorta and the inferior vena cava have been published. In each instance the predominant clinical feature has been high-output cardiac failure. It is the purpose of this paper to record the first case of an arteriovenous fistula between an atherosclerotic abdominal aortic aneurysm and an anomalously placed retroaortic left renal vein. The predominant clinical features were quite different from those of aorto-vena caval fistula. In our patient, left flank and abdominal pain was severe and associated with a pulsating abdominal mass and continuous bruit over the left side of the abdomen and back. Resection of the aneurysm and closure of the opening in the left renal vein with preservation of its continuity and insertion of a bifurcating, crimped, knitted Dacron prosthesis led to healing of the lesion and a