Objective: To study the histopathological features of mesenchymal tumors of the uterine corpus with heterologous and hematopoietic components, and review their histogenesis and differential diagnosis from other neoplastic and non-neoplastic lesions. Methods: Ten cases of mesenchymal tumors of the uterine corpus, massively infiltrated by hematopoioetic cells, or composed of other benign heterologous elements (adipose tissue in the present cases) were retrieved from the archival files of our laboratory and studied histopathologically. Immunohistochemistry was applied in selected cases. Results: Six of our studied cases were diagnosed as leiomyomas, two as lipoleiomyomas, one as a symplastic lipoleiomyoma, and one as an endometrial stromal tumor. The leiomyomas were massively infiltrated by lymphocytes (5 cases) or eosinophils (one case). Immunohistochemical study of the leiomyomas with massive lymphocytic infiltration revealed the presence of a predominantly B­cell population within the infiltrate, which was polyclonal in nature. The endometrial stromal tumor was severely infiltrated by histiocytes, and was positive for vimentin, CDlO, PgR and negative for actin, desmin, ER and caldesmon. Conclusion: The presence of hematopoietic or heterologous elements within an otherwise bland uterine leiomyoma or endome­trial stromal tumor may give rise to diagnostic difficulties. Regularity of the tumor margins, low mitotic activity and absence of nuclear atypia or necrosis should be established for the exclusion of a malignancy. In the presence of massive lymphocytic infiltra­tion of a leiomyoma the clonality of the infiltrate may aid in differentiating it from a malignant lymphoma. The pathogenesis and clinical significance of these rare neoplasms remain to be clarified.