Purpose: this study has been performed to evaluate the pathogenesis of choledochal cyst in Vietnamese children, especially the role of pancreaticobiliary common channel in forming of diseaseMaterials and methods: amylase in bile was quantities in 91 patients and peroperative cholangiography was carried out on 81 of these patients at surgical service, children hospital No 1Results: The result shows that 77.78% of cases of choledochal cyst together with pancreaticobiliary channel with the length average of 11 mm and the angle between of choledochal and pancreatic ducts measure more than 50º.