PURPOSE: To assess the accuracy of MR cholangiography(MRC) in the diagnosis of cholelithiasis, and to determine interobserver agreement. MATERIALS AND METHODS: Between March and September 1999, 43 consecutive patients with biliary obstruction [24 men and 19 women aged 25 -85 (mean, 58) years] underwent MRC using the single-shot fast spin-echo technique. Heavily T2-weighted source images(axial and coronal) 3 -5 mm thick and 12 projection images with 15- degree rotation and 5-cm thickness were obtained. All images were reviewed blindly and indepen-dently by two radiologists specialized in the interpretation of abdominal imaging information. Choledocholithiasis was evaluated in eight segments of the intrahepatic duct(IHD), extrahepatic duct(EHD) and gall bladder lumen. Final diagnosis was established on the basis of operative (n=31) and other radiological (n=12) findings. The sensitivity, specificity and accuracy of the MRC findings were assessed, and using kappa measurement (cross-table analysis,SPSS Windows for 8.0), interobserver agreement was determined. RESULTS: Thirty of the 43 patients, had choledocholithiasis (IHD stones in 7 cases, EHD stones in 15, and GB stones in 18). For radiologist 1, sensitivity, specificity and accuracy were 86%, 100% and 98%, respectively, in the diagnosis of IHD stones; 100%, 89% and 93%, respectively, in the diagnosis of EHD stones; and 81%, 96% and 91%, respectively, in the diagnosis of GB stones. For radiologist 2, the corresponding figures were 86%, 94% and 93% (1HD stones); 87%, 89% and 88% (EHD stones); and 81%, 86% and 84% (GB stones). Interobserver agreement for the diagnosis of choledocholithiasis was excellent in all cases. The kappa mesurement was 0.91 for 1HD stones, 0.77 for EHD stones, and 0.70 for GB stones. CONCLUSION: MRC is an excellent imaging modality for the diagnosis of choledocholithiasis, and interobserver agreement was also excellent.