Brenner tumor variants--such as metaplastic, proliferating, and low-malignant-potential (three categories recently designated as intermediate Brenner tumors)--and malignant Brenner tumors are unusual tumors presenting problems in classification. DNA ploidy and S-phase reflect the intermediate status of metaplastic, proliferating, and low-malignant-potential Brenner tumors. The category of "transitional cell carcinoma of the ovary" has been proposed for those primary ovarian carcinomas in which definite urothelial features are present, but no benign, metaplastic, and/or proliferating Brenner tumor is identified. Two subtypes have been described, the papillary and the malignant Brenner-like types. These tumors are more aggressive than malignant Brenner tumors, but they appear to respond better to chemotherapy than other types of ovarian epithelial cancer.