Congenital cysts of the choledochus and of the glandulae mucosae biliosae are rare anomalies generally observed in pediatric age: it is in fact exceptional to detect them in adults. There seems also to be a difference in the occurrence among the various races since the disease is more frequently seen in the Japanese and in women. In the Western world the incidence of this pathology has rated to be 1 out of 26,000 hospitalizations, consequently the personal experience and familiarity of every surgeon with this disease will be naturally limited. The authors describe the case of a women, aged 21, under observation as carrier of cystoduodenostomy after congenital cyst of the choledochus. A calculosis of the common hepatic duct as well as the stenosis of the previous cystoduodenostomy are also discovered. The abscission of the cyst and the confection of a Roux's en Y loop hepaticojejunostomy with the separation of the previous gastrojejunostomy are then performed. According to the authors, the complete abscission of the cyst and the Roux hepaticojejunostomy should be considered the surgery of choice when the local situation and the patient's general condition allow it because this treatment reduces the occurrence of late postoperative accidents such as lithiasis and cholangitis and the possibility of malignant degeneration of the cyst. Two years after the operation, the patient is in excellent health conditions.