Background: MRCP is rapidly replacing diagnostic ERCP in various pancreaticobiliary diseases. This study was designed to evaluate the accuracy of MRCP in detecting and determining the extent of choledochal cysts, as well as associated ductal anomalies or lesions. Methods: The study design was an 8- year retrospective survey conducted at a tertiary referral center, Asan Medical Center (University of Ulsan College of Medicine, Seoul, Korea). There were 72 patients with choledochal cysts. All patients underwent both MRCP and ERCP. MRCP findings were compared with those of ERCP as the criterion standard. Results: The overall detection rate of MRCP for choledochal cysts was 96% (69/72). The sensitivity, the specificity, the positive predictive value, and the negative predictive value of MRCP for classifying choledochal cysts according to Todani’ s classification were 81% , 90% , 86% , and 86% in type I, respectively; 73% , 100% , 100, and 95% in type III, respectively; 83% , 90% , 80% , and 91% in type IVa, respectively; 100% , 100% , 100% , and 100% in type IVb, respectively; and 100% , 100% , 100% , and 100% in type V, respectively. The sensitivity, the speci- ficity, and the accuracy of MRCP for detecting ductal anomalies were 83% , 90% , and 86% , respectively. The detection rate of MRCP for concurrent cholangiocarcinoma and choledocholithiasis was 87% (13/15) and 100% (8/8), respectively. Conclusions: MRCP showed overall good accuracy in the detection and the classification of choledochal cysts and revealed associated cholangiocarcinoma and choledocholithiasis with excellent accuracy. MRCP, therefore, may supersede the diagnostic role of ERCP for the patients with choledochal cysts. However,MRCPshowed limited capacity to detect minor ductal anomalies or small choledochocele. Background: MRCP is rapidly replacing diagnostic ERCP in various pancreaticobiliary diseases. This study was designed to evaluate the accuracy of MRCP in detecting and determining the extent of choledochal cysts, as well as associated ductal anomalies or lesions. Methods: The study design was an 8 - year retrospective survey conducted at a tertiary referral center, Asan Medical Center (University of Ulsan College of Medicine, Seoul, Korea). There were 72 patients with choledochal cysts. All patients underwent both MRCP and ERCP. MRCP findings were compared with those of Results: The overall detection rate of MRCP for choledochal cysts was 96% (69/72). The sensitivity, the specificity, the positive predictive value, and the negative predictive value of MRCP for classifying choledochal cysts according to Todani ’s classification were 81%, 90%, 86%, and 86% in type I, respectively; 73%, 100%, 100% and 95% in type III, respectively; 83%, 90%, 80%, and 91% in type IVa, respectively; 100%, 100%, 100%, and 100% in type IVb, respectively; and 100%, 100%, 100%, and 100% in type V, respectively. - ficity, and the accuracy of MRCP for detecting ductal anomalies were 83%, 90%, and 86%, respectively. The detection rate of MRCP for concurrent cholangiocarcinoma and choledocholithiasis was 87% (13/15) and 100% (8/8 ), respectively. Conclusions: MRCP showed overall good accuracy in the detection and the classification of choledochal cysts and revealed associated cholangiocarcinoma and choledocholithiasis with excellent accuracy. MRCP, therefore, may supersede the diagnostic role of ERCP for the patients with choledochal cysts. However, MRCPshowed limited capacity to detect minor ductal anomalies or small choledochocele.