P53 expression was studied using immunohistochemistry in patients (n=94) with pathologic stage I squamous cell lung cancer treated surgically between 1991-1992. The overall p53 positivity ratio was 48/94. 83 of the cases proved to be suitable for follow-up analysis carried out in November, 1995. 46/83 were p53 positive, and 25/46 patients were alive at the time of analysis. The patients who died (21/46) had a mean survival time of 17.5 months. In p53 negative cases (37/83), however, 29/37 patients were still alive at the time of follow-up, and 8/37 had died with a mean survival time of 23.1 months. A significant correlation could be found between p53 immunopositivity and reduced survival time (p=0.0125). Interestingly, out of 83 cases analyzed histologic evidence of tuberculous scar tissue was present in 9 tumors with a p53 positivity ratio of only 1/9. When flow cytometry was used to examine tumor samples from all subgroups mentioned above (n=32), no correlation was found between the p53 immunopositivity or the prognosis and the DNA content of tumor tissues. Our results suggest that in the early stage of squamous cell lung cancer the p53 positivity may be an indicator of a more aggressive tumor behavior and a shortened survival time.