Uterine tumors resembling ovarian sex cord tumors are rare neoplasms of unknown etiology that are classified as distinct from endometrial stromal tumors on the basis of their morphologic, molecular, and behavioral characteristics. These neoplasms have a variable immunophenotype, sometimes coexpressing epithelial, myoid, and sex cord markers. To date, only 2 cases of uterine tumors resembling ovarian sex cord tumors associated with tamoxifen use have been reported. Here, we report the case of a 49-year-old woman who had been using tamoxifen for 5 years to treat breast cancer. The tumor was initially diagnosed by hysteroscopy biopsy on the basis of morphologic and immunohistochemical features. Hysterectomy revealed a polypoid mass measuring 20 mm. After an 18-month follow-up, the patient remains disease free. Here, we review the clinical, pathologic, and immunohistochemical features of uterine tumors resembling ovarian sex cord tumors and endometrial stromal tumors with a sex cord component associated with tamoxifen treatment.