Abstract： Background Choledochal cyst is rare in western countries. The relatively high incidence of coexistent hepatobiliary disease increases the difficulty of the surgical management of choledochal cyst. Here we analyze the diagnosis and treatment of congenital bile duct cyst in 122 Chinese adults.Methods The clinical data of 122 patients with congenital choledochal cysts admitted from 1981 to 2006 were analyzed.Results Clinical symptoms in most cases were nonspecific, resulting in delayed diagnosis. Sixty-one patients (50%) had coexistent pancreatobiliary disease. Among the 122 patients, 119 patients underwent ultrasonic examination;ERCP/MRCP was performed in 63 cases and CT in 102 cases. Abnormal pancreatobiliary duct junction was found in 48 patients. Sixteen patients had malignant lesions in the bile duct, arising in 11 of them from incomplete choledochal cyst that underwent various operations including cystenterostomy or cystojejunostomy. There was significant difference between the patients who underwent incomplete cyst resection and complete cyst resection in malignancy rate of bile duct (Chi square test, P= 0.000; odds ratio, 7.800; 95 % confidence interval, 2.450 to 24.836).Conclusions ERCP, CT and MRCP had proved their great values in the classification of the disease. Cyst excision with Roux-en-Y hepaticojejunostomy is recommended as the treatment of choice for patients with type Ⅰ or type Ⅳ cysts. For type Ⅴ cyst (Caroli's disease) with recurrent cholangitis, liver transplantation should be considered.