Three cases of poorly differentiated endometrial adenocarcinoma showing trophoblast-like differentiation are reported. The multinucleated, syncytiotrophoblast-like cells were strongly positive for beta-human chorionic gonadotropin (beta-HCG) by immunohistochemical study. High levels of beta-HCG were also present in the patients' serum, but dropped significantly after treatment. The patients had an unusually rapid and progressive clinical course with widespread dissemination and death by tumor.