The aims of this study were to evaluate the effectiveness of magnetic resonance cholangiography (MRC) in diagnosing patients with cholestasis and to compare these results to those obtained with endoscopic retrograde cholangiopancreaticography(ERCP). From January 1996 to December 1998 a total of 85 consecutive patients who were candidates for ERCP because of a suspected diagnosis of mechanical cholestasis were included in this study. All patients underwent MRC and consecutive ERCP 24 to 48 hours later. The sensitivity for detecting common bile duct stones was 93%,specificity 74%, positive predictive value 89%, and negative predictive value 82%. For the determination of tumorous bile duct stenosis the sensitivity and specificity were both 100%. MRC might be an ideal method for evaluating patients with unclear laboratory or ultrasonography findings before laparoscopic cholecystectomy, thereby avoiding unnecessary invasive diagnostic tests with possible harmful complications.