The clinicopathologic features of five cases of müllerian adenosarcoma of the uterus are presented and are compared with those of previously reported cases. Four tumors were localized in the endometrium; in one case, a cervical or endometrial origin was not clear. The ages of the patients ranged from 53 to 79 years. Two died without clinical evidence of recurrence 19 and 18 years after hysterectomy. One was alive and well 10 years postoperatively and one was lost to follow-up 6 months after therapy. In one case, a first abdominal recurrence was resected 5 years and 9 months after hysterectomy; the patient died of a second abdominal recurrence 18 months later. The tumors were bulky polypoid masses producing metrorrhagia. Histologically, a sarcomatous component was intimately associated with benign epithelium of various müllerian types. The neoplasm was typically organized in papillary fronds and periglandular sarcomatous cuffs. Cystic glands were also a constant feature. Mitoses were generally fewer than 10 per 10 high-power fields, except in one case where they were 44 in a more malignant-appearing area. Adenosarcoma must be differentiated from other müllerian tumors, mainly carcinosarcoma whose prognosis is much less favorable.