Tumors of the uterus resembling ovarian sex cord tumors were reported by Clement and Scully in 1976 and were divided in 2 groups: group 1, endometrial stromal tumors, and group 2, mural uterine tumors-both with elements resembling ovarian sex cord tumors. In the former, the sex cord component constitutes a minor portion of an endometrial stromal neoplasm, whereas in the latter, it is the predominant or exclusive component of a uterine wall lesion composed of a variety of mesenchymal elements. An origin from endometrial stromal cells, adenomyosis, stromal myosis, endometriosis, or multipotential cells within the myometrium was postulated in both groups of tumors. In group 1 tumors, the prognosis depends on the type, grade, and stage of the underlying stromal neoplasm. Group 2 tumors seemed to be benign, although because of the occasional recurrence of these tumors, they should be considered of low-grade malignant potential. In recent years, the histological features in group 2 were found to be much more varied than those in group 1 and consisted among others of retiform areas, glomeruloid structures, and Leydig-like cells. In group 1 tumors, the sex cord elements remained limited to cords, trabeculae, nests, and tubules. Eventually, the abbreviation ESTSCLE, or endometrial stromal tumors with sex cord-like elements, was given to group 1 tumors, whereas UTROSCT, or uterine tumor resembling ovarian sex cord tumor, was used for group 2 tumors. The most significant information in recently conducted studies concerns the immunophenotype of these lesions especially of UTROSCT. Out of the plethora of the immunohistochemical stains, a panel of 4 including calretinin, inhibin, CD99, and Melan A has emerged which seemed to be the most characteristic sex cord markers. Positivity for calretinin and at least for 1 of the other above-mentioned markers may thus confirm the diagnosis of UTROSCT. Endometrial stromal tumors with sex cord-like elements, on the other hand, usually express only 1 sex cord marker, mostly calretinin. However, additional studies are necessary to confirm these observations. In conclusion, UTROSCT and, to a lesser degree, ESTSCLE, are polyphenotypic neoplasms, which, according to the evidence available at present, most likely arise from pluripotential uterine mesenchymal cells. In UTROSCT, the differentiation into sex cord components is predominant or exclusive, whereas in ESTSCLE, it is minor.