Eleven biphasic uterine tumors with epithelial components and homologous stroma were reevaluated. Originally these were diagnosed as adenofibroma, adenosarcoma, carcinosarcoma, or mixtures thereof, but were now reclassified as adenosarcomas of which seven were "pure" and four mixed with foci of carcinosarcoma. Nine of the tumors arose in the endometrium and two in the endocervix. The mean patient's age was 55 years. The most common complaint was vaginal bleeding. Macroscopically these tumors presented as polypoid masses. The epithelial component consisted mainly of endometrial, endocervical, ciliated, and clear cells. Squamous metaplasia and focal hyperplasia were occasionally observed. Malignant epithelial change was only present in foci of carcinosarcoma. The stroma showed prominent cellular periglandular cuffs, occasionally round solid or perivascular nodules, and areas of focal or diffuse stromal hypercellularity. In all these areas stromal cells were atypical and/or pleomorphic. Stromal foam cells were seen in three cases. Mitotic activity was low ranging from one to three mitoses per 10 high power fields (HPF). Follow-up was negative exept in two cases with recurrence and abdominal metastases. It was concluded that stromal hypercellularity with atypism and pleomorphism in periglandular, perivascular location as well as of focal or diffuse nature, is characteristic of uterine adenosarcoma. Adenofibromas present a fibro-collagenous stroma lacking the crowded cellular areas. Mitotic activity is too variable to serve as a reliable diagnostic criterion. Uterine adenosarcomas are usually tumors of low grade malignancy but the lack of correlation between histologic appearance and biologic behaviour precludes prognostication in the individual patient.