Leydig cell tumors of the ovary are very rare, frequently associated with symptoms of virilization in postmenopausal patients. It is sometimes difficult to localize the tumor precisely even with modern imaging techniques. A 62-year-old patient presented with recent onset of rapidly progressive virilization including increased hirsutism, progressive balding, deepening voice and enlargement of the clitoris. Initial laboratory examination revealed a total serum testosterone level of 1330 ng/dL. Serum dehydroepiandrosterone sulfate, androstenedione and 17 hydroxyprogesterone levels were all within normal limits. Extensive preoperative evaluations included transvaginal ultrasound, abdominal Computed tomography and magnetic resonance imaging failed to localize the tumor. Therefore, selective ovarian venous hormonal sampling (SOVHS) was performed and they revealed that the total serum testosterone level was significantly higher in the left than in the right ovarian vein (7000 ng/dL vs. 225 ng/dL). A total abdominal hysterectomy and bilateral salpingo-oophorectomy was performed. Microscopic examination of the left ovary revealed a Leydig cell tumor.