Ultrasound is widely advocated as the initial noninvasive imaging study in evaluating suspected biliary obstruction. Some have suggested using ultrasound as the sole diagnostic test before exploratory laparotomy. To evaluate the accuracy of ultrasound in determining the level and etiology of biliary obstruction in patients with biliary dilatation, and to define its role in the evaluation of these patients, we performed a retrospective review of all patients from August 1986 to August 1991 who had biliary dilatation by ultrasound and subsequent endoscopic retrograde cholangiopancreatography and/or a percutaneous transhepatic cholangiography. Forty-two patients were included in this study, and ultrasound delineated the level of obstruction in 88 per cent, defined the etiology of the obstruction in 48 per cent, and diagnosed choledocholithiasis in 33 per cent of patients with this condition. A literature review revealed that ultrasound has a sensitivity of 71 per cent in delineating the level of obstruction, a sensitivity of 57 per cent in defining the etiology of biliary obstruction, and detects choledocholithiasis in 32 per cent of patients with this condition. We conclude that ultrasound is a highly accurate diagnostic test for delineating the level of biliary obstruction. Ultrasound should be the initial radiographic test in the evaluation of the patient with suspected biliary obstruction to guide further radiographic evaluation.