A 67-year-old man was admitted with severe back pain and bilateral lower limb swelling. Enhanced computed tomography showed an infrarenal abdominal aortic aneurysm (92 × 75 mm(2)) and a short aortocaval fistula (7 mm). Immediately afterward, circulatory collapse occurred, and the patient was rushed to the operating theater. A much larger aortocaval fistula (22 × 35 mm(2)) than that demonstrated by preoperative computed tomography was found and was repaired with a Dacron patch while using two balloon-tipped catheters to control bleeding. Then, the abdominal aortic aneurysm was replaced with a bifurcated graft. The patient's postoperative course was uneventful. In this case, enhanced computed tomography detected the aortocaval fistula, but could not assess its size accurately. Successful surgical repair of an aortocaval fistula depends on early accurate delineation of the fistula and prompt control of bleeding.