A case of benign cystic mesothelioma in a 53-year-old woman is presented. The patient had abdominal pain and a palpable mass for 4 days. This mass was noticed incidentally by an obstetrician. A computed tomographic scan of the abdomen and pelvic sonography showed a cystic mass, 6 x 4 cm, in the right lower quadrant close to the cecum and suggested cystadenocarcinoma of the ovary. Operation showed that the mass involved peritoneum in region of the appendix. Complete removal of the mass was done. Grossly it consisted of multilocular cyst containing clear, serous, gelatinous fluid. The light microscopic examination revealed that this lesion consisted of cystic spaces of various size and intervening connective tissue stroma. The cells lined the cysts varied from flattened to cuboidal with occasionally a picket-fence or hobnailed appearance in areas. Brush borders were seen on the luminal surface of some cells. Electron microscopic examination confirmed that the cells were mesothelial origin. This lesion mimics cystic lymphangioma of the abdomen grossly and light microscopically, from which differential features are discussed.