A group of 133 primary oral squamous cell carcinomas were studied concerning a relationship between exposure factors and tumour biological parameters with a focus on the TP53 gene and p53 protein status. Tumours were evaluated using immunohistochemistry (IHC) for expression of p53, PCNA, Ki-67 and bcl-2 proteins. The TP53 gene was studied for mutations using PCR amplification of exons 5-9 and single strand conformation polymorphism (SSCP) analysis. The collected data were correlated to the exposure factors smoking, oral snuff, liquor, oral infections, dental factors, dental X-ray and iron deficiency. When compared with matched controls only oral infections, and reported HSV-infections in particular, gave statistically significant ORs (odds ratio) for all tumours (OR 8.0) as well as for the group of IHC p53 positive tumours (OR 12). No association between smoking and p53 positivity was found (OR 1.0).