A retrospective review of CT scans in 69 consecutive patients with proven biliary obstruction due to both malignant and benign causes was performed to define and differentiate CT changes. Abrupt termination of a dilated extrahepatic biliary duct was characteristic of a malignant process in the absence of a mass. Gradual tapering of a dilated duct was specific for benign disease. Other findings, such as degree of intra- or extrahepatic duct dilatation and presence or absence of a dilated pancreatic duct were not reliable in distinguishing benign from malignant causes. The authors also found CT to be accurate in detecting common duct stones with a sensitivity exceeding 80%.