Cyclins and wild-type p53 protein are prime cell cycle regulators and may be involved in tumorigenesis. Cyclin A is a late S cyclin and its abnormalities have been reported in several cancers, including oral squamous cell carcinomas. To explore whether aberrant G1/S in p53 mutant tumours leads to increased cyclin A protein in oral squamous cell carcinomas (OSCC), a total of 39 samples were evaluated for the expression of cyclin A and p53 protein by an immunohistochemical method using a labelled polymer assay. These samples comprised two hyperkeratotic and three oral premalignant lesions (two moderate and one severe dysplastic lesions), and 27 OSCC, together with seven healthy controls. The results demonstrated that the cyclin A protein was localized and highly expressed in the nuclei of the tumour cells. Although there was no correlation between cyclin A detection and the local lymph node involvement, a positive correlation was noted between the positivity of cyclin A and p53 protein (p <0.05). The results suggested that cyclin A may contribute to the progression of oral cancer and correlated to some degree with that of the p53 gene activity.