Background: There has been controversy regarding the histogenesis of Brenner tumors. It is generally accepted that Brenner tumors are derived directly from ovarian surface epithelium, which undergoes metaplasia to form the typical urothelial-like com­ponents, whereas some investigators assume that Brenner tumors arise from immature germ cells. Case: We describe a well-documented case of the coexistence of struma ovarii regarded as a form of teratoma and Brenner tumor in the same ovary. Immunohistologically, not only columnar cells of thyroid follicles, but also transitional cells of Brenner nests were positive for thyroglobulin. Conclusions: In the present case, Brenner tumors and thyroid elements coexisted and were positive for thyroglobulin. While there is strong evidence that pure Brenner tumors originate mostly from the ovarian surface, at least Brenner tumors associated with ter­atomatous elements may have a germ cell origin.