A 29-year-old woman presented with secondary amenorrhea, primary infertility, and virilization, which had developed over the past 2 years was suspected to have a virilizing tumor at her left ovary. Her serum testosterone level was markedly elevated (380 ng/dL). Left salpingooophorectomy was performed, and histopathological examination revealed a thecoma of the left ovary. The postoperative serum testosterone level returned to 65 ng/dL. The patient did not have regression of virilism soon. However, the patient had a normal menstruation 29 days after surgery and gave birth to a baby 13 months after surgery.