Mixed müllerian tumors of the uterus, which have been divided into homologous and heterologous types, are considered neoplasms of high malignant potential. In the heterologous variety, the presence of rhabdomyosarcoma has been associated with an especially poor prognosis. We report the first case of a heterologous, malignant mixed mesodermal tumor (adenocarcinoma, stromal sarcoma, and rhabdomyosarcoma) confined to an endometrial polyp. The patient, treated by surgery only, remains clinically free of disease 11 years later. Mixed mullerian tumors of limited extent may not be associated with the dismal prognosis that usually accompanies such lesions.