A case of diffuse adenomatoid tumor of the uterus in an immunosuppressed renal transplant recipient is reported and compared with two previously reported, similar cases. The multinodular uterine lesion grossly resembled intramural leiomyomata except for a mucoid cut surface and a cystic serosal component. The predominant patterns of the tumor were adenoid and angiomatoid with less prominent solid and cystic patterns. Immunohistochemical and ultrastructural studies confirmed the mesothelial nature of the tumor cells. Additionally, there was strong diffuse immunoreactivity for proliferating cell nuclear antigen, a low expression of Ki-67, and weak nuclear p53 staining. The relationship between immunosuppression and diffuse adenomatoid tumors is discussed.