With approximately 150 reported cases, fistulas between the abdominal aorta and inferior vena cava are rare. Preoperative clinical diagnosis of aortocaval fistula is difficult because the classical triad of abdominal pain, pulsatile abdominal mass, and abdominal machinery-like bruit may be absent in up to 50 % of patients. We report a case of aortocaval fistula complicating abdominal aortic aneurysm which was diagnosed preoperatively using breath-hold gadolinium-enhanced three-dimensional MR angiography.