Many studies have been focused on cytogenetic and molecular genetic defects in brain tumors; therefore the role of ATM as a tumor suppressor gene in these tumors is poorly considered. In this study mutation analysis of exon 19 and 39 of ATM gene and P53 accumulation were investigated by PCR-SSCP, sequencing, and flow cytometry . Four polymorphisms including D1853N, IVS 38-8 T?C, F858L, P872T were reported for the first time in brain tumors other than medulloblastoma. Expression of P53 could be detected in more than 10% of cells in patients affected with meningioma and 4.08% and 3.46% of cells inastrocytoma and chordoma respectively. The present findings could confirm the importance of ATM gene alterations in tumor genesis of brain tumors and further investigation is essential.