The development of a cystadenocarcinoma from previously benign cystadenoma is controversial. Neither clinical nor biological factors have been described to explain this transformation. High levels of serum and cystic CEA and CA 19-9 seem to help in the diagnosis of cystadenoma but not cystadenocarcinoma. Definitive histological evaluation is the only means to discriminate malignant from benign cysts. We report a case of cystadenoma of the liver with very high cystic levels and normal serum levels of CEA and CA 19-9.