Eighteen cases of primary trabecular carcinoid of the ovary were analyzed from a clinicopathologic viewpoint. The patients ranged in age from 24 to 74 years and presented with symptoms of an ovarian mass; none had the carcinoid syndrome. Although the carcinoid always proved to be unilateral, the contralateral ovary was sometimes enlarged by a dermoid cyst. The carcinoid usually formed a small mass in an otherwise obvious dermoid cyst, but in six instances it formed a large, solid mass, and in 2 of these cases no other teratomatous elements could be demonstrated. The prognosis was nearly always favorable after removal of the neoplasm, although 1 patient had a recurrence after 2 years and died after 51/2 years. Primary trabecular carcinoids are characterized by a distinctive pattern of ribbons of argentaffin cells and should not be confused with a Sertoli-Leydig cell tumor, a strumal carcinoid, or a metastatic trabecular carcinoid.