It is well-established that a high incidence of p53 mutations exist in oral cavity squamous cell carcinomas (OCSCCs). To determine whether p53 mutations are etiologically associated with OCSCC development or are associated with exposure to specific carcinogens, we have analyzed the conserved regions of the p53 gene (exons 5-9) in 48 OCSCCs obtained from patients with varied tobacco and alcohol use histories by polymerase chain reaction/single strand conformational polymorphism (PCR/SSCP) and DNA sequencing analysis. Thirty-eight percent (18/48) of the OCSCCs exhibited a mutation in exons 5-9 of the p53 gene. There was a significantly higher incidence of p53 mutations in OCSCCs from tobacco users (predominantly cigarette smokers) compared to those who had never used tobacco. No increase in the incidence of p53 mutation was observed in tobacco users who drank alcohol. G to A transitions and deletions were the predominant mutations observed in OCSCCs from tobacco users. No specific pattern of mutation was observed in OCSCCs from those subjects who had never used tobacco. These data suggest that a history of tobacco use was associated with a high incidence of p53 mutations in patients with OCSCC and that tobacco carcinogens include a specific pattern of mutations in oral cavity tissue in vivo.