The case of hilus cell tumor of the ovary occurs rarely. The hallmark feature of the hilus cell tumor is virilization because of testosterone overproduction by this neoplasm. A 73-year-old postmenopausal woman with high plasma testosterone levels and virilization was demonstrated by frontal balding, hirsutism, acne and hoarseness. Investigation of the cause of virilization on this patient revealed an elevated serum testosterone level and an increased left ovary. Following bilateral salpingo-oophorectomy, a 3.0 x 2.0 x 1.5 cm left ovary was found to contain a hilus (Leydig) cell tumor. One week after operation, the testosterone level was 0.8 ng/ml (1.8 to 7.58 ng/ml). The related literature concerning the clinicopathological features of hilus cell tumor was also reviewed.