Endometrial stromal tumors are uncommon mesenchymal tumors of the uterus. The classification of these tumors has evolved and the most current World Health Organization classification (2003) divides these neoplasms into: endometrial stromal nodule, low-grade endometrial stromal sarcoma, and undifferentiated endometrial sarcoma. The salient clinicopathologic features of these tumors are described, and a comprehensive review of literature pertaining to potential prognostic factors in endometrial stromal sarcomas is provided. Clinical factors, including age, race, parity and menopausal status, and pathologic factors, including tumor size, tumor stage, nuclear atypia, mitotic activity, tumor necrosis, lymphovascular space invasion, DNA ploidy and proliferative activity, and expression of hormone receptors, have been explored with varying outcomes. Surgicopathologic stage seems to be the most important prognostic factor in low-grade endometrial stromal sarcomas. The impact of other prognostic factors on survival is unclear or controversial, especially in patients with stage I tumors.