BACKGROUND/AIMS: In spite of various diagnostic modalites, biliary cystic neoplasms (biliary cystadenoma and cystadenocarcinoma) remain to be difficult to diagnose preoperatively. Recently, there are some reports that elevated CA19-9 level in serum and/or cystic fluid could be a useful finding in the differential diagnosis of biliary cystic neoplasm. This study aimed to evaluate the expression of CA19-9 and to elucidate its significances in intrahepatic biliary cystic neoplasms and simple hepatic cysts. METHODS: In 8 patients with biliary cystic neoplasms and 6 simple hepatic cysts, symptoms, radiologic and laboratory findings were reviewed retrospectively. In 5 biliary cystic neoplasms (4 bililary cystadenomas, 1 biliary cystadenocarcinoma) and 5 simple hepatic cysts, immunohistochemical stainings for CA19-9 were performed with formalin-fixed, paraffin-embedded tissues. RESULTS: In 8 biliary cystic neoplasms, two cases were suspected as biliary cystadenoma preoperatively and 6 cases could not be distinguished from simple cysts or cholangiocarcinoma preoperatively. In 6 simple hepatic cysts, 3 cases were diagnosed preoperatively and 3 cases could not be distinguished from biliary cystadenoma or pancreatic pseudocyst preoperatively. Expression of CA19-9 in simple hepatic cysts and biliary cystic neoplasms were 80% in both groups. Expression of CA19-9 is not related to the elevated level of CA19-9 in serum. CONCLUSINOS: Our data suggests that the elevated level of CA19-9 in serum may not be helpful in the preoprative diagnosis of biliary cystic neoplasm.