The two major susceptibility genes, BRCA1 and BRCA2, are involved in hereditary breast and ovarian cancer syndrome. Early detection of mutation carriers has crucial clinical importance, as it allows identification of women who may benefit from intensive clinical follow-up or prophylactic surgery. Generally accepted inclusion criteria for BRCA1/2 mutation testing are based either upon family history of breast or ovarian cancer or young age at cancer diagnosis. In order to analyze the impact of BRCA1/2 mutations on breast cancer development in the Czech population and to confront the clinical and histopathological data of mutation carriers with current criteria for mutation testing we examined the frequency of mutations in unselected breast cancer cases. Mutational analysis of BRCA1/2 genes performed in 679 unselected female breast cancer patients included all recurrent deleterious alterations previously identified in the Prague area and truncating mutations in the whole exon 11 of BRCA1. Within analyzed gene sequences more than 80% of mutations were identified previously in high-risk patients. A total of 16 breast cancer patients (2.4%) carried a mutation. BRCA1 mutations were identified in 14 (2.1%) whereas BRCA2 in 2 (0.3%) women. Family history of ovarian cancer was a strong predictor of a BRCA1/2 mutation (OR = 8.3; p = 0.01), however, family history of breast cancer was not indicative of carrier status. A significant association between medullary breast cancer and mutation status was observed. Current criteria for BRCA1/2 mutation testing would distinguish only 6 out of 16 (37.5%) carriers identified in our study. Ten breast cancer patients with confirmed BRCA1/2 germ-line mutation exhibited no clinical characteristics that would predict their carrier status. Therefore, we believe that the testing for BRCA1/2 mutations in the Czech Republic may not be restricted only to high-risk patients. Our results indicate that analysis of locally prevalent BRCA1/2 mutations in all breast cancer patients might extend substantially the percentage of identified mutation carriers.