Biliary cystadenomas and cystadenocarcinomas are rare tumors of biliary origin and constitute less than 5% of the total intrahepatic cysts of bile duct origin. They occur most commonly in middle age females. Clinical manifestations are non-specific, so these tumors are incidentally found during autopsy or surgery. The ultrasonogram, abdominal CT scan, angiography and aspiration cytology are valuable diagnostic methods. The typical sonographic appearance of these tumors is a large intrahepatic globular or ovoid thick-walled cystic mass which often contains multiple septations or papillary infoldings. The characteristic CT appearance of these tumors is similar to that of a low-density intrahepatic mass which may cantain mural nodule or internal septation. However, regardless of the diagnostic modalities, pre-operative diagnosis as well as intra-operative one is difficult. Since biliary cystadenocarcinomas are believed to arise from benign cystadenornas, complete surgical resections, if possible, is a warranted method to avoid malignant change of these tumor. We report one of biliary cystadenocarcinoma canfirmed by the operation with review of the literatures. (Korean J Gastroenterol 1998;31:701-706)