Carcinoma of the biliary tract is a rare complication of choledochal cysts. Furthermore, the greater predisposition of the cyst wall to neoplastic change has been cited as additional justification for cyst excision rather than on-site internal drainage as the primary choice of operation. The report concerns a patient who developed cholangiocarcinoma despite excision of a choledochal cyst and presented with symptoms of biliary obstruction within one year of the operation. Although this is a rare complication, the need for careful long-term follow-up is supported by this observation.