Numerical aberrations of chromosome 17 were studied by fluorescence in situ hybridization (FISH) using pericentromere specific DNA probe in 27 oral squamous cell carcinomas (SCCs), and its relationship with p53 and Bcl-2 protein expression was investigated. Since cells with polysomy 17 are significantly increased in SCC (p = 0.0005), chromosome 17 abnormality seems to be correlated with carcinogenesis of oral SCC. Chromosome 17 abnormality varied from case to case, and the degree of the abnormality did not correlate with the stage of the disease, the histological differentiation of SCC, or relapse of the disease and lymph node metastasis. However, there was a correlation between polysomy 17 and p53 immunoreactivity (p = 0.0228). p53 immunoreactivity showed a correlation with relapse of the disease (p = 0.0441). An inverse relationship was found between p53 and Bcl-2 immunoreactivity (p = 0.0421). In conclusion, we suggest that polysomy 17 is closely related carcinogenesis of oral SCC, and with p53 overexpression. It is assumed that polysomy 17 correlates with the mutation of p53 which results in an accumulation of aberrant p53 protein, and that its activation causes an increase of p53 protein.