Although choledochal cyst is generally considered a disorder of childhood, in approximately 20% of patients a cyst is first recognized in adult life. We reviewed nine adults who underwent operation for choledochal cyst from 1974-1985 at Yale New Haven Hospital. Presenting symptoms included: crampy right upper quadrant pain, jaundice, pruritus, cholangitis, pancreatitis, hepatomegaly, and elevated liver function tests. Seven patients had undergone previous biliary surgery. The eight patients with type I cysts underwent complete excision of the cysts with Roux-Y choledochojejunostomy. One patient with a type IVa cyst underwent Roux-Y cystjejunostomy. All patients had complete resolution of biliary symptoms. There were no deaths, serious complications, or development of biliary malignancy in the 6 months to 13 years of follow-up. Optimum treatment of choledochal cyst is complete excision with reconstruction by Roux-Y choledochojejunostomy.