Thirteen endometrioid carcinomas of the ovary with predominant patterns resembling those of sex cord-stromal tumors are reported. Eight of these neoplasms had been misinterpreted by the referring pathologists as sex cord-stromal tumors, almost always of the Sertoli-Leydig cell type. The latter diagnosis was suggested by a predominance of small tubular glands or winding, elongated solid tubular structures. In four cases, the presence of luteinized cells in the tumor stroma contributed to the misinterpretation. Each specimen, however, had one or more features establishing its endometrioid nature, including large tubular glands resembling those of the typical endometrioid adenocarcinoma, foci of squamous differentiation, luminal mucin accumulation, and adenofibromatous components. Two tumors were bilateral. The age range of the patients (from 58 to 86 years) differed markedly from that of patients with Sertoli-Leydig cell tumors, who are generally much younger, as did the associated clinical manifestations, which were those of ovarian cancer in general. No androgenic effects were observed and estrogenic manifestations were evident in only one of the cases.