The prognostic significance of p53 immunoreactivity in adult patients with supratentorial fibrillary astrocytic neoplasms was examined by Kaplan-Meier survival analysis. Using a monoclonal antibody that reacts with both mutant and wild-type p53 protein (PAb 1801), reactivity was assessed immunohistochemically in specimens from the first diagnosis of astrocytic neoplasm in 95 patients: 26 astrocytomas (A), 19 anaplastic astrocytomas (AA), and 50 glioblastomas multiforme (GBM). Overall, 53% of cases exhibited any p53 nuclear immunoreactivity, with approximately the same proportion in each histologic grade. Survival was measured from diagnosis to death or last follow-up and ranged from 3 months to 9 years. Histologic grade was a powerful prognostic variable for this group of patients (p < 0.001), with median survivals of 88, 18, and 9 months for A, AA, and GBM patients, respectively. In contrast, patients with p53-immunoreactive or -nonimmunoreactive neoplasms had median survival times of 18 or 15 months, respectively (p = 0.21). These results indicate that p53 immunoreactivity was not prognostically significant in this group of adult patients with supratentorial fibrillary astrocytic neoplasms, although a small difference in survival cannot be excluded.