Mature cystic teratomas are common benign tumors of the ovary. The most common form of malignant transformation is squamous cell carcinoma, however, malignant transformation is rarely observed and cases are usually asymptomatic. Carcinoid tumors are rare tumors of the neuroendocrine system. A number of the carcinoids result in clinical syndromes due to the secretion of vasoactive substances produced by the tumor. A 75-year-old woman suffering from groin pain was admitted to the Faculty of Medicine at Bezmialem Vakif University (Istanbul, Turkey). An adnexal mass was detected during the physical examination. Magnetic resonance imaging scans exhibited an 8x7-cm mass in the right ovary. Surgical excision of the mass was performed and histopathological examination revealed a mature cystic teratoma with three germ layers. An area consisting of nests and trabeculae was evident in the cyst wall. The pathological diagnosis was of an insular and trabecular variant of carcinoid tumor arising in a mature cystic teratoma. The patient did not present with carcinoid syndrome, and no recurrence was observed after 11 months of follow-up examinations.