The aim of this investigation was to study the prevalence of p53 gene mutations in male and female breast cancers and to find out the relationship between this event and p53 protein expression. Genomic p53 was amplified by polymerase chain reaction (PCR). Exons 5-8 were screened for mutations using single stranded conformation polymorphism (SSCP) analysis. P53 protein expression was detected by immunohistochemistry (IHC) with the monoclonal antibody DO-1. In female breast cancer, p53 gene mutation was detected in 33% cases in either exon 5 or 6. However, in male, mutation was detected only in exon 6 in 90% cases. On the other hand, p53 protein expression was observed in all of these cases. Moreover, p53 protein immunostaining was observed in some of those cancer tissues, where no mutation was detected in exons 5-8. P53 dysfunction, as indicated by mutation or increased protein expression, common in both male and female breast cancer, but rate of occurrence or site of mutation differ from each other. Our results in male breast tumors indicate a positive correlation between p53 mutation and p53 protein overexpression, whereas the results in female breast tumors indicate an overexpression of p53 protein even without p53 gene mutation. Therefore, it may be presumed that p53 protein accumulation can result primarily from mutation. In addition, stabilization of p53 through binding to other proteins is another possible reason of p53 overexpression.