The great majority of Brenner tumors are benign, but a few are frankly malignant. The rare proliferating Brenner tumor is a third variant intermediate between the benign and malignant forms. Characteristic areas of this tumor show an unusual degree of epithelial proliferation and morphologically resemble low‐grade (papillary) transitional cell carcinoma of the urinary bladder. The papillary tumor tends to grow within cystic spaces, and the epithelial component does not invade the tumor stroma. In our 3 cases, adjacent areas of typical Brenner tumor were observed. The tumors were all confined to the ovary, and none has recurred or metastasized. In one case, the patient has been free of tumor for 8 years. These tumors give additional support to the concept that Brenner tumors are composed of epithelium of urinary tract (urothelial) type.