Endometrial Stromal Sarcomas are rare neoplasms, accounting for 0.2% of female genital tract malignancies. They occur predominantly in post menopausal women, although they can develop during the reproductive years or even in childhood. The most important prognostic factors are the patient's age at diagnosis, FIGO surgical stage, myometrial invasion, mitotic index, DNA index and tumoral necrosis. In this study we try to evaluate the main prognostic factors in the women treated in the Portuguese Oncology Institute in Oporto. From the study of the 14 patients with the diagnosis of endometrial stromal sarcoma, between 1974 and 1995, we can conclude that the main factors influencing the outcome were FIGO surgical staging, mitotic index and myometrial invasion.