Transitional cell carcinomas (TCCs) of the endometrium are rare, and only 10 cases have been described to date. We report the case of a 46-year-old woman who developed both a TCC of the endometrium and a benign ovarian Brenner tumor. Such an association has not yet been reported in the literature. Immunohistochemical studies of the uterine tumor showed cytokeratin 7 positivity and cytokeratin 20 negative staining, which was consistent with a Müllerian derivation. Human papilloma virus (HPV) immunostaining as well as polymerase chain reaction (PCR) analysis using primers for HPV types 6, 11, 16, and 18 failed to detect viral DNA. The coexistence of a TCC of the endometrium and an ovarian Brenner tumor might be coincidental but raises the possibility of a field effect, as seen with multifocal endometrioid tumors or multiple urinary tract TCCs.