Alterations of the p53 gene are the most frequently documented genetic abnormalities in human cancer. The aim of the present study was to analyse if this alteration is an early event in oral tumorigenesis and if the suprabasal expression of p53 is a marker of the presence and severity of epithelial dysplasia. Immunohistochemical p53 expression in 78 specimens of oral squamous cell carcinoma and non-tumoral adjacent epithelium was analysed. Non-tumoral epithelium was observed in 53 cases (67.9 per cent), being normal in six cases (7.6 per cent), hyperplastic in 24 cases (30.7 per cent) and dysplastic in 48 cases (61.5 per cent). Epithelial dysplasia was mild (23 cases, 47.9 per cent); moderate (23 cases, 47.9 per cent) and severe (two cases, 4.1 per cent). Twenty-one cases of the dysplasias (43.8 per cent) expressed p53. No p53 expression appeared in any normal epithelium. Basal p53 expression always appeared in mild dysplasias (two cases). Suprabasal p53 expression appeared in mild and moderate dysplasias in nine cases and in one severe dysplasia. No statistical correlation was observed between suprabasal expression of p53 and the presence or severity of the dysplasia. The expression of p53 is an early event in oral tumorigenesis but it does not behave as an objective marker of the presence or severity of epithelial dysplasia.