We investigated the association of p53 abnormalities (gene mutations by DNA sequencing and protein over-expression by immunostaining) with clinical data and prognosis in 74 patients with resected non-small cell lung cancer (NSCLC). DNA analysis of exons 5-8 of the p53 gene showed 34 mutations in 74 resected primary NSCLC (45.9%). Immunohistochemical study of the p53 protein revealed that 41 of 74 (55.4%) samples had positive staining. We found strong agreement between the results of the p53 protein expression test (p53-PE) and the p53 gene mutation test (p53-M) (Cohen's kappa = 0.65, 95% CI 0.48-0.82). Joint distribution of the results (analysed using the bivariate Dale model) was mainly influenced by, histological type of tumour. A positive result for the p53-PE test significantly increased (estimated odds ratio 84.5; 95% CI 8.89-803.03) the odds of observing a positive result in the p53-M test. In the univariate analysis (log rank test), positive results in the p53-M test and the p53-PE test were significantly associated with overall survival (P < 0.001 and P = 0.005, respectively). In the multivariate analysis (Cox's proportional hazard model), a positive result for the p53-M test significantly increased relative risk for overall survival (RR 9.56; 95% CI 2.62-34.87; P < 0.001). When the result of the p53-M test was accounted for, a positive result for the p53-PE test did not offer any additional prognostic information due to the strong dependence of results of the tests. However, when the result of the p53-M test was removed from the model, a positive result for the p53-PE test became a significant unfavourable prognostic factor (P = 0.009). We conclude that p53 gene mutation and protein expression analyses are in a strong agreement. Joint distribution of the results depends mainly on histological type of tumour. When considered separately, both tests are unfavourable prognostic factors in NSCLC. When the result of the p53-M test is taken into account, the p53-PE test does not offer any additional prognostic information.