AIM: The mutations in two breast cancer susceptibility genes, BRCA1 and BRCA2, are frequently associated with familial breast cancer. In this study, we aimed to investigate the probable founder mutations of BRCA1 and BRCA2 genes in Iranian breast cancer patients. METHODS: The total 400 patients affected with primary breast cancer were included in this study. Mutation detection was carried out on the basis of a PCR-based amplification, and two founder mutations for BRCA1 (185delAG and 5382insC) and one for BRCA2 (6174delT) were screened and considered by pedigree analysis. RESULTS: The positive family histories of breast cancer and other malignancies were recorded in 27.5% and 52% of patient pedigrees, respectively. The most frequent occurrence of breast cancer across four generations revealed to be 50% in the 1st degree in the 3rd generation, 68.8% in the 2nd degree in the 2nd generation, and 59.5% in the 3rd degree in the 3rd generation. Only 185delAG mutation in the BRCA1 gene was found in 2/400 (0.5%) of investigated pedigrees. There were two sisters of the same family. To our interest both sisters carried 185delAG mutation in the BRCA1 gene, which had a complete penetrance. However, the mutation was observed with two different organ targeting, at almost an early age of onset (proband: 45 yr, her sister: 30 yr). CONCLUSION: Considering the importance of genetic counseling and recording, the adequate information for the pedigrees of cancer patients put forward the principle approaches in cancer clinics to facilitate early detection for preventing challenges.