Caroli's Disease (CD) is a rare congenital disorder characterized by cystic dilatation of the intrahepatic bile ducts. This report describes a patient with cholangiocarcinoma arising in the setting of monolobar CD. In spite of detailed investigations including biliary enteric bypass and endoscopic retrograde cholangiography, the diagnosis of mucinous cholangiocarcinoma (CCA) was not made for almost one year. The presentation, diagnosis and treatment of monolobar CD and the association between monolobar CD and biliary tract cancer are discussed. Hepatic resection is the treatment of choice for monolobar CD.