Objective To investigate the role of ataxia telangiectasis mutated（ATM） gene in the oncogenesis and progression of oral squamous cell carcinoma（OSCC）. Methods A total of 61 formalin- fixed and paraffin- embedded samples were obtained from patients with hyperkeratosis, oral leukoplakia, OSCC and normal healthy controls. The expression of ATM protein in all of the samples was investigated by streptavidin- peroxidase immunohistochemistry assay. PCR was also performed to detect the loss of heterozygosity（LOH）in D11s2179 of ATM gene. The correlations between ATM and the clinical and histopathological characteristics were also investigated. Results The results indicated that the ATM expression was increased in oral premalignant lesions（P
