In 1959, Swerdlow reported a case of a 27-year-old woman with a pelvic tumour that seemed to arise from the peritoneum, in the presence of normal ovaries, fallopian tubes and uterus, and that was histologically similar to papillary serous carcinoma of the ovary [52]. Since then several authors have described this disease using different names, such as extraovarian primary peritoneal carcinoma (EOPPC), peritoneal papillary serous carcinoma, peritoneal adenocarcinoma of Müllerian type, serous surface papillary carcinoma, normal sized ovary carcinoma syndrome, peritoneal mesothelioma, and primary peritoneal carcinoma. This illustrates the confusion about definition, histogenesis and clinicopathologic features of this entity. In 1993, in an attempt to sort out these confounding variables, the Gynecologic Oncology Group (GOG) developed criteria to define EOPPC: - Both ovaries must be either physiologically normal in size or enlarged by a benign process. - The involvement in extraovarian sites must be greater than the involvement on the surface of either ovary. - Microscopically, the ovarian component must be one of the following: non existent; confined to ovarian surface epithelium with no evidence of cortical invasion; involving ovarian surface epithelium and underlying cortical stroma but with tumour size less than 5x5mm within ovarian substance with or without surface disease. The histological and cytological characteristics of the tumour must be predominantly of the serous type that is similar or identical to ovarian serous adenocarcinoma of any grade [8, 55].