Choledochal cysts are congenital or acquired lesions of the biliary tree with a cystic dilatation of the bile duct. We experienced a choledochal cyst accompanying acute pancreatitis caused by anomalous pancreaticobiliary ductal union(APBDU) in a 2 year old boy. The choledochal cyst associated with APBDU is rarely encountered in the clinical field, and thus we report this case with the presentation of abdominal ultrasonogram, computed tomogram, and intraoperative cholangiogram. A brief review of choledochal cyst associated with APBDU is also presented.