Granular cell tumors involving the female reproductive tract are rare, with only a small number of cases described. Of the reported cases, none are documented within an ovarian mature cystic teratoma (MCT). This report documents a case of a granular cell tumor, incidentally discovered within an ovarian MCT in a 50-yr-old woman undergoing a supracervical hysterectomy and left salpingo-oophorectomy. Although malignant transformation and other secondary ovarian neoplasms in MCT have been well documented, synchronous nonovarian benign neoplasms are reported much less frequently. The histogenesis of secondary tumors arising in MCT is incompletely understood, and the current case provides additional insight, especially pertaining to schwannian and neuroectodermal tumors arising in this setting. The current case, to the best of our knowledge, represents the first report of a granular cell tumor involving a mature teratoma of any site, with the diagnosis being supported by morphologic and immunohistochemical staining characteristics.