We report on the clinical and pathologic findings in 31 cases of adenosarcoma of the uterus subjected to hysterectomy and staging laparotomy. Nine of 30 patients (30%) have had recurrent tumor and six of 30 (20%) have already died of tumor in a relatively short follow-up period (mean, 38.3 months). Seventeen of 31 cases were diagnosed as adenosarcoma with sarcomatous overgrowth (SO). Ten of these 17 with SO contained focal or extensive rhabdomyosarcoma. In six cases, extrauterine spread was identified as follows (two patients had two sites each): vaginal involvement (two cases), pelvic lymph node metastases (two), positive peritoneal cytologic findings (two), parametrial invasion (one), and ovarian metastasis (one). Extrauterine spread (stage III) (p less than 0.001) and myometrial invasion (p = 0.04) were associated with higher rates of recurrence. The presence of lymphatic and/or vascular invasion, SO, and rhabdomyosarcomatous differentiation also indicated poor prognosis but did not attain statistical significance. Based on this experience, staging laparotomy including peritoneal cytology is suggested in cases of clinical stages I and II adenosarcoma. The differential diagnosis of these tumors is also discussed.