Rare cases of virilization caused by ovarian tumors with functioning stroma have been reported, typically during pregnancy. The authors report a case of a post-menopausal 60-year-old woman who presented with breast tenderness and vaginal bleeding and was found to have an 18.4-cm adnexal mass by imaging. Cystectomy revealed a benign mucinous cystadenoma with stromal luteinization associated with elevated estradiol levels and features of hyperestrinism. Due to the high clinical suspicion of a malignancy, a total abdominal hysterectomy with bilateral salpingo-oophorectomy and appendectomy was performed. These hormonally induced changes must be recognized to avoid misinterpretation of a malignancy.