A total of 103 consecutive patients with suspected biliary obstruction were studied using both computed tomography (CT) and ultrasound (US) to evaluate the relative accuracy of the methods. In 47 patients with confirmed obstruction, CT and US were comparably accurate in differentiating obstruction from nonobstruction. The precise level of obstruction was identified by CT in 88% and by US in 60%; the cause of obstruction was accurately predicted by CT in 70% and by US in 38%. Both methods detected useful additional information, such as cholelithiasis or retroperitoneal adenopathy. The authors use US as a screening examination; if there is doubt about the level and cause of sonographically demonstrated obstruction, CT has proved to be an accurate means of further evaluation.