Cystic dilatation of the biliary tree, so called choledochal cyst, is an uncommon disease and is not uncommonly associated with carcinoma. The most symptoms on. presentation are abdominal pain, weight loss, jaundice, and palpable mass. The prognosis of these lesions is dismal. Recently we experienced a case of carcinoma arising in a choledochal cyst in 27-year-old male complaining jaundice and fever. ERCP revealed marked dilated the CBD and obstruction of the proximal portion of the CHD. A computerized tomographic scan and percutaneous cholangiogram showed cystic dilatation of both intrahepatic ducts and solid mass in the left hepatic duct. The patient was treated with surgical resection. Pathologic studies disclosed an adenosquamous carcinoma.