Ten cases of congenital cystic dilatation of the common bile duct (including insufficiency form) were examined for mode of pancreatico-biliary anastomosis and cholangiographic findings. The results were as follows. Male to female ratio was 1:9 in this series. Regarding the mode of pancreatico-biliary anastomosis, type I (pancreatic duct flowing into common bile duct) tended to occur frequently in patients 30 years old or more, while type II (common bile duct flowing into pancreatic duct) in patients under 30 years old. With respect to clinical symptoms, no cases had triad (jaundice, abdominal pain and palpation of mass), but abdominal pain occurred in all the cases. Jaundice and palpation of mass were seen in 30% and 10% of the cases, respectively. Regarding the age at the onset and the duration of the disease, type I occurred in elderly cases with a longer duration of disease, while type II occurred in young cases with a shorter duration of disease. The degree of distention increased in proportion to the severity of the peripheral stenosis of the biliary duct. Complication with biliary tract carcinoma was seen in 2 type I cases. Among the type I cases, those with mild distention were considered to be insufficient form.