We have encountered four cases of an unusual variant of well-differentiated endometrioid carcinoma that was predominantly composed of tubules, solid or hollow, as well as cord-like areas histologically mimicking Sertoli and Sertoli-Leydig cell tumors. The two features most helpful in differential diagnosis were the presence of areas of tumor with the typical confluent pattern of endometrioid carcinoma, and the presence of mucin at the apical borders of the tumor cells and/or within glandular lumina. Other features that were helpful if present, but were observed only in one case each, were foci of squamous metaplasia or the presence of ciliated epithelium. In two cases, ultrastructural studies showed well developed microvilli and perinuclear microfilaments confirming the endometrioid nature of the neoplasm. The patients varied from 22-74 years in age. All tumors were confined to a single ovary, and no tumor is known to have recurred or metastasized. One of the patients died at age 80, six years following operation, presumably without evidence of recurrent neoplasm or metastases. Two other patients are living and well, one and 14 years after diagnosis. In one patient follow-up is short. The clinicopathologic features of this variant of endometrioid carcinoma are reviewed with emphasis on differential morphologic features.