Choledochal cysts are congenital malformations and can be classified into four types. The type 1 lesion is the usual form; the others are extremely uncommon. The treatment in most cases should be surgical drainage into the gastrointestinal tract, preferably using the jejunum in Roux-en-Y fashion. The presence of a carcinoma within the cyst requires excision of the cyst if technically feasible as this offers the best hope for cure. The role of prolonged exposure of the cyst epithelium to stagnant bile in the etiology of the carcinoma has not yet been settled. Two patients with carcinoma in a choledochal cyst were treated at the New York Hospital—Cornell Medical Center.