The prognostic value of proliferative activity and DNA distribution (ploidy), determined by flow cytometry (FCM), was evaluated in 38 cases of human malignant neuroepithelial tumors. No statistically significant correlation was found between flow cytometric data and clinical outcome. In particular, there was no significant difference between mean survival in cases with percentage of cells in S-phase lower and higher than 5%, respectively. In 21 cases with unimodal DNA distribution, the mean survival was 11.7 months; in 17 cases with bimodal DNA distribution, the mean survival was 12.5 months. The difference was not statistically significant. In our experience, proliferative activity and ploidy do not correlate well with the clinical course and survival of patients with malignant neuroepithelial tumors. However, application of FCM may provide, aside from histopathologic examination, additional biologic information that may be valuable in understanding the variation observed in the course of individual patients.