A 73-yr-old woman had noted progressive virilization. The plasma testosterone levels were elevated (340 ng/dl) and the pelvic ultrasound examination revealed an enlarged left ovary. At laparotomy, a large cystic tumor replaced the left ovary. The plasma testosterone became normal after the removal of the tumor. On anatomical analysis, the tumor was an ovarian cystadenoma with hyperplasia of stromal cells in the periphery of the tumor.