Endodermal sinus tumor (EST) arising in the endometrium is an extremely rare malignant neoplasm. To the authors' knowledge, this is only the second report of an EST arising in this location. The tumor was exophytic, 2.4 cm in diameter, and was located in the fundus uteri. It had infiltrated the circumambient endometrium slightly. Preoperative serum alpha-fetoprotein (AFP) levels were markedly elevated, 1580 ng/ml. The patient received a simple abdominal hysterectomy and bilateral salpingo-oophorectomy followed by combination chemotherapy consisting of vincristine, actinomycin D, and cyclophosphamide. To date, there has been no evidence of tumor recurrence, and serum AFP titers, which had returned to normal 7 weeks after surgery, continue to remain within normal limits. We believe this is the first successful treatment of a documented case of primary EST of the endometrium.