PURPOSE: Choledochal cyst is a rare malformation of the pancreatobiliary ductal system, manifested by dilatation of biliary tree with or without anomalous insertion of the common bile duct into pancreatic duct. The purpose of this study is to review the incidence of anomalous pancreatobiliary union(PBU) and the shape of common bile duct based on the angle of pancreatic duct and common bile duct union. MATERIALS AND METHODS: We analyzed cholangiopancreatographic findings of 21 patients with choledochal cyst, emphasizing PBU. The PBU was classified into acute-angled PBU, right-angled PBU, normal PBU, and unknown PBU on the basis of common bile duct insertion to pancreatic duct. The shape of common bile duct dilatation was evaluated with regard to angle of PBU. RESULTS: Fourteen of 21 patients had anomalous PBU with slender or ectatic form of common channels. Three patients had normal opening of common bile duct and pancreatic duct, and in remaining 4 patients the PBU was not visualized. Among 14 patients with PBU, 5 patients had right-angled PBU and 9 patients had acute-angled PBU. Cystic form of common bile duct dilatation was seen in 13 patients and cylindrical form was in 8 patients. Cystic dilatation of common bile duct was seen in 4 patients out of 5 right-angled PBU. CONCLUSION: Patients with choledochal cyst had high incidence of anomalous PBU with common channel (67%). The shape of common bile duct dilatation was cystic in 62% of patients, and the right-angled PBU was prone to be cystic dilatation(80%).