Arteriovenous fistulas between the common iliac vessels resulting from spontaneous rupture of aneurysms are rare, with only 31 cases having been reported since 1971. Clinical diagnosis is possible when a unique set of findings is present, namely high-output cardiac failure, a pulsatile abdominal mass associated with a bruit or thrill, and unilateral arterial insufficiency or venous engorgement. Recently, with advancements in diagnostic techniques, the number of cases in which an arteriovenous fistula is found between the common iliac vessels has increased. Diagnosis can be difficult, however, as in the case of one of our patients in whom the predominant sign was acute renal failure. Other reports of renal failure or impairment in the presence of a common iliac fistula have also appeared. Awareness of this phenomenon can help the physician to establish the diagnosis when one or more of the classic signs are absent. Prompt diagnosis and surgical management have contributed to the high incidence of survival in patients with arteriovenous fistulas between the common iliac vessels.