Choledochal cyst is rare in the western countries, but common in oriental countries. Complicatioins include ascending cholangitis, recurrent pancreatities, progressive biliary cirrhosis, portal hypertension, stone formation and later malignant transformation. Bile peritonitis secondary to rupture is one of the rarest complications, with an incidence of 1.8 % to 18 %. The anomalous arrangement of the pancreatobiliary ductal system with a long common channel may cause inflammation leading to perforation of the cyst. The authors found 4 cases (14.2 %) of bile peritonitis among 28 cases of choledochal cyst treated from Jan. 1983 to Jan. 1998. The patients ages ranged from 6 months to 3 years and three were female. The perforation sites were located on the common bile duct at its junction with the cystic duct in 2 cases, the distal cyst wall in 1 case and the left hepatic duct at its junction with cyst in 1 case. The types of choledochal cysts by Todani's classification were Type IVa in 3 cases and type I in 1 case. By the new Komi's classification utilizing operative cholangiogram there were 2 cases of Type Ia, 1 case of type IIb and 1 case of type III. One stage cyst excision and hepaticojejunostomy(Roux-en Y type) was done in 3 cases, and two staged operation in 1 case. All patients had an uneventful course postoperatively. The average day of discharge was 9.8th postoperatively. In conclusion, primary excision of the choledochal cyst and biliary reconstruction is a safe and effective treatment of ruptured choledochal cyst in infants.