Objective To study the diagnosis, therapy and prevention of bile duct carcinomas in choledochal cysts. Methods We retrospectively analysed clinico pathologic data, the ways of operation and living time of 11 patients with bile duct carcinomas in choledochal cysts in two hospitals from 1986 to 1997. Results There were complete excision of the choledochal cysts associated with choledochojejunostomy in 4 patients, exploration of bile duct and drainage with T shape tube in 3 patients. And there were also the excision of the wall of bile duct cysts and the tumor and cholangioplasty, choledochocystoduodenostomy, biopsy, pancreaticoduodenectomy and cholangiojejunostomy at the porta hepatis, resection of original rhynchostoma of choledochojejunostomy in one patient, respectively. One patient has lived for 3.6 years after radical resection. Others lived for 13.6 months after operation. Conclusions It is the key of improving and lengthening lives to find this disease in the early stage and to resect radically as early as possible.