DNA ploidy status, as determined by flow cytometry, has been useful in predicting survival in certain malignancies. Between January 1975 and January 1985, 85 cases that met the inclusion criteria-pathologic stage I endometrial adenocarcinomas, primary surgical therapy, endometrioid cell type, and adequate paraffin-block samples-were analyzed by DNA flow cytometry. Depth of myometrial invasion, tumor grade, and presence of lymphatic vascular space invasion were established in all cases. Ten of the 85 tumors (12%) were aneuploid. The median follow-up was 9 years with a range of 2 to 16 years. There were 9 recurrences with 5 deaths from cancer, and 8 patients died of intercurrent disease. The relative hazards for recurrence associated with aneuploidy, S-phase fraction, grade 3 histology, and any myometrial invasion were 3.1, 3.18, 3.2, and 4.9, respectively, but did not reach statistical significance. Because of the low recurrence and mortality rate in this homogeneous group, a larger sample will be necessary to fully establish a role for DNA ploidy status in identifying a poor prognostic subset.