Choledochal cysts in children and adults may behave differently. To identify these differences the records of 49 patients (22 children and 27 adults) who underwent surgery for choledochal cysts over a period of 7 years were analysed retrospectively. In two adult patients who had undergone a previous cholecystectomy an acquired malformation could not be excluded. Cholangitis was more common in adults. Choledochal cysts in children were predominantly Type I cystic lesions, whereas Type IV cysts were more common in adult patients. Anomalies of the pancreatic duct and associated hepatobiliary problems were seen exclusively in adults and the latter can make excision of the cyst more difficult and complicated. To prevent the development of complications choledochal cysts should be excised as soon as they are detected.