The accepted technique for diagnosing choledocholithiasis at the time of cholecystectomy is operative cholangiography. Reports in the surgical literature suggest that intraoperative ultrasound can replace operative cholangiography in the accurate detection of common duct stones. This prospective study was performed jointly by radiologists and surgeons together in the operating room. Twenty-one patients underwent intraoperative ultrasonography and operative cholangiography at the time of cholecystectomy. In the 16 cases in which both studies were adequate, there were 11 in which no stones were seen on either; three in which stones were seen on both; and two in which stones were diagnosed by sonography alone. In one of these latter cases, the stones were confirmed, making the cholangiogram falsely negative. In the other case, no stones were found so we presume that sonography was falsely positive. Although this technique can be accurate and useful, it is technically demanding, even for an experienced sonologist. We feel that this technique is likely to be of benefit only to the surgeon with considerable ultrasound training, expertise, and motivation.