Nine cases of endometrial stromal sarcoma are described. Four of the patients were categorized as having a uterine endolymphatic stromal myosis (ESM) with less than 10 mitoses per 10 HPF and five patients as having an endometrial stromal sarcoma (ESS) with more than 10 mitoses per 10 HPF. Another prognostic distinction based on the degree of stromal differentiation is also discussed. The symptomatology, diagnostic means, clinical features, and treatment are described.