Breast cancer susceptibility gene (BRCA1) is known to be responsible for hereditary breast and ovarian cancer. This gene is highly penetrant conferring a risk for 0.92 by the age of 70. Germline mutation in this gene leads to susceptibility to breast and ovarian cancer, with a genotype phenotype correlation. Frequency of mutations of this gene in normal population of breast cancer is low suggesting that the effort of primary screening for BRCA1 gene should be restricted to only familial cases with a strong history of breast and ovarian cancer. Recent studies indicate that BRCA1 is a tumor suppressor gene responsible for both normal development and carcinogenesis of the breast. Normal function elucidated so far, reveal BRCA1 to be a multifunctional protein involved in DNA repair, cell cycle regulation and transcription. There is circumstantial evidence that gene interacts with p53, a protein involved in cell cycle control, DNA repair and apoptosis.