The clinicopathologic findings in 24 cases of Brenner tumors of the ovary, seen at the University of Michigan Medical Center between 1941 and 1975, are reported. Abnormal uterine bleeding was the most common presenting symptom. Associated endometrial changes ranging from glandular hyperplasia to invasive adenocarcinoma were found in 5 cases. No consistent relationship was found between the thecomatous appearance of the stroma of the tumor and endometrial changes suggestive of estrogen stimulation. Seven patients had other types of ovarian neoplasms. Four patients had bilateral Brenner tumors. Three Brenner tumors were histologically and clinically malignant. This study suggests that the presumed potential steroidogenesis of the Brenner tumors of the ovary may not always be a product of the thecalike cells of the stroma. The need for further biosynthetic studies is reemphasized. Furthermore, when conservative therapy of a benign Brenner tumor is attempted, the contralateral ovary should be carefully examined and a wedge resection considered. The optimal therapy of malignant Brenner tumors has not been established; adequate surgery and careful staging followed by individualized adjuvant therapy is recommended.