Primary serous papillary carcinoma of the peritoneum is a rare neoplasm arising from the mesothelium. Histologically it is indistinguisable from ovarian serous papillary carcinoma, but it should be free of tumor or involved only superficially with the ovary. Radiologically its common findings are peritoneal and omental masses with ascites, and it is indistinguisable from peritoneal carcinomatosis or malignant mesothelioma. We report a case of surgically proven primary serous papillary carcinoma of the peritoneum in a 63-year-old woman.