In this study, we present the clinicopathologic features and immunophenotypic characteristics of five cases of uterine tumors resembling ovarian sex cord tumors and three cases of endometrial stromal tumors with sex cord-like elements, with emphasis on immunohistochemical markers of sex cord differentiation. The mean patient age was 42 years (range 19-69 years), and vaginal bleeding was the most common clinical presentation. The tumors were usually polypoid masses arising in the uterine fundus, with a mean tumor size of 6.7 cm. Sex cord patterns in uterine tumors resembling ovarian sex cord tumors, including anastomosing cords, trabeculae, small nests, tubules, and in one case, a striking retiform architecture with Leydig-like cells, comprised from 70 to 100% of the tumor volume. All uterine tumors resembling ovarian sex cord tumors were positive for two or more markers of sex cord differentiation; all five cases showed strong immunoreactivity for calretinin, with coexpression of CD99 (four cases), Melan-A (two cases), and inhibin (two cases). Endometrial stromal tumors with sex cord-like elements were less frequently positive for markers of sex cord differentiation, with each case positive for one marker (calretinin, two cases; CD99, one case). In addition, all eight cases were frequently positive for cytokeratin, CD10, vimentin, estrogen receptor, and progesterone receptor; desmin immunoreactivity, when present, was limited to minor foci of smooth muscle. Overall, the morphologic and immunohistochemical findings in uterine tumors resembling ovarian sex cord tumors strongly support that these unusual uterine tumors are polyphenotypic neoplasms with true sex cord differentiation.