Transitional cell tumors of ovary are composed of epithelial cells that resemble urothelium. They make up 1-2% of all ovarian neoplasms. The group includes benign Brenner tumor, borderline Brenner tumor (no stromal invasion), and malignant Brenner tumor (unequivocal stromal invasion). The borderline and malignant subtypes contain a component of benign Brenner tumor. The tumors previously called transitional cell carcinomas of the ovary (not associated with benign or borderline Brenner tumor component) are now classified as variants of high-grade serous carcinomas. Transitional cell ovarian tumors arise directly from the ovarian surface epithelium that has undergone transitional metaplasia. Rare cases may have their origin in germ cells.