We present the results of a clinicopathologic study of 109 patients with endometrial stromal sarcoma and eight patients with endometrial stromal nodule. Of the 109 patients with endometrial stromal sarcoma, follow-up was obtained on 93 (85%). The stage distribution of the patients with stromal sarcoma and the number of patients with follow-up (numerator) compared to the total number of patients in each stage (denominator) are: Stage 1, 73/85; Stage II, 3/6; Stage III, 11/11; Stage IV, 6/7. Stage II patients are considered separately in the analysis. Thirty-six percent of the Stage I patients experienced one or more relapses. Of these, six (23%) died of disease from 11 to 360 months from diagnosis (median, 79 months). Nine (35%) were alive with disease. Of the eleven Stage III patients, eight had one or more relapses and of these, six died of disease. Of the six Stage IV patients, five had one or more relapses and of these, three died of disease. The outcome differences between Stages I, III, and IV are statistically significant (p less than .01). Microscopic features evaluated included the mitotic index (MI = number of mitoses/10 high-power fields) and cytologic atypia. Forty-five percent of Stage I patients who had both rare mitotic figures and minimal atypia had one or more relapses and of these, two (13%) died of disease at 85 and 360 months, respectively. Thus, neither MI nor cytologic atypia were predictive of tumor recurrence for patients with Stage I tumors.