We describe a case of a concomitant well-differentiated endometrial endometrioid adenocarcinoma and leiomyosarcoma of the uterus in a 66-year-old woman who presented with a 6-month history of vaginal bleeding. The patient underwent total hysterectomy for endometrial carcinoma diagnosed by endometrial biopsy. Gross examination of the specimen revealed an endometrial mass bulging into the endometrial cavity and an underlying well-circumscribed nodule separated from the endometrial mass by a myometrial band. Frozen section performed at the time of the total hysterectomy rendered a diagnosis of malignant mixed-müllerian tumor. Histologic examination of the permanent sections revealed well-differentiated endometrial endometrioid adenocarcinoma clearly separated from a high-grade leiomyosarcoma. Differential diagnosis included malignant mixed-müllerian tumor. However, no admixture of carcinomatous and sarcomatous elements was present. There were no heterologous elements. To the best of our knowledge, no similar case has been described in the English literature.