Although p53-gene mutations occur with significant frequency in diffuse low-grade and high-grade astrocytomas, and are postulated to play an important role in tumorigenesis in these cases, the role of the p53 gene in pilocytic astrocytomas remains unclear. Published data using DNA-based assays for p53-gene analysis in these tumors have shown contradictory results in mutation frequency (0-14%). It is not known whether these heterogeneous results stem from the biological diversity of this tumor group or from technical problems. To re-evaluate p53-gene status in pilocytic tumors, we analyzed 18 tumors chosen to represent the clinical and biological heterogeneity of this tumor type with respect to anatomical location, patient age, gender, ethnic origin (Caucasian or Japanese) and the concomitant occurrence of neurofibromatosis type 1 (NFI). All primary tumors were histologically diagnosed as pilocytic astrocytoma (WHO grade 1), except for one anaplastic pilocytic astrocytoma (WHO grade III) which developed in an NFI patient and recurred as glioblastoma multiforme (WHO grade IV). p53 mutations were detected using an assay in yeast which tests the transcriptional activity of p53 proteins synthesized from tumor mRNA derived p53-cDNA templates. None of 18 tumors, including 3 NFI-related tumors, showed p53-gene mutations between and including exons 4 and 11. We conclude that p53-gene mutations are extremely rare findings in pilocytic astrocytomas, and are absent even in those exceptional cases in which malignant progression of such tumors has occurred.