Ovarian endometrioid carcinomas with sertoliform features (SECs) are infrequent and often misinterpreted as sex cord-stromal tumors. The clinicopathologic features and immunohistochemical expression of keratin, epithelial membrane antigen (EMA), inhibin, and estrogen and progesterone receptors were evaluated in 13 cases of SEC. The women were 41 to 89 years of age (mean, 60 yr) with abdominal enlargement secondary to a unilateral ovarian mass as the most frequent clinical presentation. One patient displayed virilization. At presentation, 10 patients were Stage I, one was Stage II and two were Stage III. The tumors were composed of compact anastomosing cords and small tubules embedded within a fibrous stroma. Nuclear features were Grade 1 or 2 in all but one tumor. Areas of conventional endometrioid carcinoma were observed in 12 cases. An adenofibromatous component comprising 5 to 60% of the lesion was present in seven cases. All 12 cases examined immunohistochemically were positive for keratin and EMA and negative for inhibin with focal, luteinized stromal cells positive for inhibin in 10 cases. Estrogen and progesterone receptors were positive in 10 and 11 cases, respectively. Follow-up on 6 of 10 patients with Stage I and the one patient with Stage II disease displayed no evidence of disease 10 to 120 months (mean, 57 mo). Progressive disease and death occurred at 12 and 72 months only in the two women with Stage III disease, one of which had an associated serous carcinoma in the contralateral ovary. Adequate sampling, a careful search for areas of conventional endometrioid carcinoma, and immunohistochemical studies (including EMA, keratin, and inhibin) are helpful in the evaluation of ovarian tumors with sex cord-stromal features. SEC should be considered a well-differentiated endometrioid carcinoma despite the presence of a solid, sex cord-like proliferation, with a good prognosis when confined to the ovary.