Primary malignancies of the fallopian tube are extremely uncommon, in part due to (admittedly arbitrary) definitional criteria. By convention, epithelial tumors that involve the ovary or peritoneal surfaces are considered to have arisen either in the ovary or endometrium or, in absence of significant ovarian or endometrial involvement, in the peritoneum, irrespective of whether or not the fallopian tube mucosa is also involved. Evidence from the World Health Organization and more recently, from case-control studies of BRCA mutation carriers suggests the fallopian tube may have a more direct role in the development of at least some of these carcinomas. An alternative hypothesis for the origin of ovarian and peritoneal carcinoma has even been proposed, based on the concept of transport and implantation of malignant cells from the tube to the ovary and peritoneum. Malignancies in the fallopian tube can therefore be classified as (1) arising primarily in the fallopian tube, either from preexisting endometriosis (or more rarely, a mature teratoma) or directly from tubal mucosa with metastasis to adjacent tissues; (2) arising in the ovary, endometrium, or peritoneum with metastasis to the tubal serosa or mucosa; or (3) arising primarily in the fallopian tube as well as in the ovary, endometrium, or peritoneum (simultaneous primary tumors). Since there are currently no evidence based criteria for distinguishing primary tubal carcinoma from primary ovarian or primary endometrial carcinoma in patients with high stage disease, the Association of Directors of Anatomic and Surgical Pathology recommended strategies for assignment of site of origin are based on current standard practices.