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Cytoplasmic accumulation of wild-type p53 in tumor cells indicates that the tumor suppressor is inactive with regard to growth suppressive functions. Whether this occurs randomly during tumor development or characterizes a certain tumor cell subset is not known. Here we assayed primary glioblastomas for expression and subcellular localization of p53 and determined a correlation with expression of intermediate filament proteins characterizing glial cell development. Sixty-nine percent of the tumors were p53 positive in immunohistochemistry. A significant number of tumors (23%) accumulated wild-type p53 in the cytoplasm, which correlated with the presence of vimentin and glial fibrillary acidic protein, except for 1 case. Tumors with exclusive nuclear p53 contained none or only one of these intermediate filament proteins. In an alternative approach, tumors positive for glial fibrillary acidic protein were screened for expression of p53 and vimentin. Thirty-eight percent of these tumors showed cytoplasmic p53, and all of those also expressed vimentin. Tumors with only nuclear p53 were vimentin negative, except for 1 case. No mutation was detected in p53 exons 5 to 8 in tumors with cytoplasmic p53, suggesting that they express wild-type p53. The data indicate that a cytoplasmic accumulation of wild-type p53 in human primary glioblastomas correlates with a certain intermediate filament protein expression, suggesting that it identifies a certain subset of tumors.