Eighty-three cases of nasopharyngeal carcinoma were evaluated for the presence of Epstein-Barr virus (EBV) infection in tumor cells by in situ hybridization to EBER1 transcripts, and for p53 expression by immunostains using the D07 antibody which detects native and mutant forms of the p53 protein. A highly significant association was found between EBV infection and p53 overexpression (P = .0004), with 77% of cases coexpressing both markers. This newly discovered association suggests that EBV is not an innocent bystander with respect to p53 accumulation. One possible mediator of the interaction between EBV and p53, viral BZLF1, was not colocalized with p53 in these tumors, suggesting that BZLF1 is not the factor responsible for p53 accumulation. From an epidemiological standpoint, this series of cancers represents an international cohort in which cases from an endemic part of the world (Hong Kong) were examined alongside cases from the United States, where the disease is 50-fold less prevalent. The cancers from Hong Kong tended to be less differentiated and more frequently associated with EBV, suggesting that biological differences might underlie epidemiological variations in tumor prevalence. Finally, we examined 18 potential premalignant lesions of the surface epithelium of the nasopharynx. Although our numbers are small, our data suggest that p53 accumulation might precede EBV infection in the transition from metaplasia to carcinoma in situ. Further studies are needed to dissect the stepwise progression of nasopharyngeal carcinogenesis.