Eight cases of uterine müllerian adenosarcoma with sex cord-like elements (SCEs) occurred in patients 22-85 years of age (median, 41) who presented with abnormal uterine bleeding. Seven patients had hysterectomy; one had curettage and radiation only. The polypoid endometrial tumors were composed of adenosarcoma admixed with SCEs; the latter accounted for 5-50% of the tumor. The SCEs were multifocal in six cases and formed a solitary mass at the base of the adenosarcoma in the remaining two cases. Benign-appearing epithelial-type cells, often containing abundant eosinophilic or foamy, lipid-rich cytoplasm, were arranged in solid nests, trabeculae, and solid or hollow tubules. Myometrial invasion was observed microscopically in six cases. Of seven patients with postoperative follow-up information, six were alive with no evidence of recurrent tumor at postoperative intervals of 3-11 years. The patient treated only by curettage and radiation had persistent intrauterine tumor at 7 months and died of an unrelated illness at 16 months. This study indicates that occasional uterine adenosarcomas contain SCEs similar to those described in endometrial stromal tumors and uterine tumors resembling ovarian sex cord tumors. The clinical and pathologic features of these tumors are otherwise similar to those of typical uterine adenosarcomas.