A 24-year-old woman who had one month history of right upper quadrant abdominal mass and pain was admitted to our hospital. Examination by abdomen ultrasonography and computerized tomo graphy indicated that it was a large cystic tumor in the liver with multiple internal septation. Thus she received a laparotomy. A 15 ×12 ×5 cm cystic mass from left medial segment of the liver wa noted and could be removed by cystectomy and partial segmentectomy. On cut section, yellowish serous fluid containing multilocular cyst surrounded by a smooth and glistening wall was seen Microscopic findings revealed that it is a case of intrahepatic biliary cystadenoma with mesenchyma stroma. This tumor was noted with strikingly elevated serum level of the tumor-associated antigen CA 19-9 (500 U/ml). Twenty days after the surgery, the serum CA 19-9 level returned to normal (29 U/ml). This may be a valuable finding in the differential diagnosis, so we report this case with review of the literatures. (Kor J Gastroenterol 1999;33:854 - 858)