Biliary mucinous cystadenoma of the liver is a rare tumor that develops almost exclusively in women. Its typical localization is near the hepatic hilus. It may become malignant, and therefore careful histological examination of the entire resected specimen is mandatory. Incomplete excision results in recurrence and occasionally in malignant alteration. The authors present a 66-year old woman who presented with the right upper abdominal pain and occasional vomiting, and who was diagnosed with cystic lesion of the right lobe of the liver. The lesion was totally excised by an open operation. It was filled with mucinous viscous fluid and there was proliferation in one part of the internal surface. The cystic lesion communicated with the common hepatic duct through a tiny duct (above the cystic duct), but in spite of that, it did not contain bile. Histological examination showed mucinous cystadenoma with focal malignant alteration. After the uneventful recovery, the pain and vomiting were eliminated and she has remained symptom free so far.