PURPOSE: The purpose of this study was to prospectively compare the clinical applicabillity of magnetic resonance cholangiography(MRC) with that of endoscopic retrograde cholangiography(ERC) in the evaluation of combined choledocholithiasis in patients with gall stones who were candidates for laparoscopic cholecystectomy. MATERIALS AND METHODS: Twenty-seven patients with gall stones underwent fast spin-echo MR cholangiography using the half-Fourier acquisition single-shot turbo spin echo(HASTE) method, and half-Fourier rapid acquisition using the relaxation enhancement(RARE) method. Within five hours the same patients underwent ERC. The results of MRC was reviewed by two radiologists blinded to the results of ERC. The number and size of CBD stones and gall stones, and the degree of CBD dilatation, as seen on HASTE and RARE images, were compared with the results of ERC. RESULTS: MRC depicted common bile duct stones in 10 of 11 patients shown by ERC to have stones, while in the 16 patients in whom ERC did not reveal stones, MRC demonstrated the same finding. The number of CBD stones was exactly demonstrated by HASTE imaging in eight of eleven patients(73%) and by RARE imaging in ten of eleven patients(91%) in whom ERC revealed choledocholithiasis. The size of common bile duct stones visualized by ERC correlated in nine of eleven patients(82%) on HASTE images and in seven of eleven(64%) on RARE images. MRC showed CBD dilatation in all patients in whom dilatation was demonstrated by ERC. CONCLUSION: For the evaluation of choledocholithiasis before laparoscopic cholecystectomy in patients with gall stones, MRC and ERC are equally accurate. A comparison of HASTE imaging with RARE imaging, as used in the diagnosis of choledocholithiasis, revealed no significant differences.