In the last 15 years, our understanding of genes that predispose to breast cancer has increased enormously. Germline alleles have been identified that have a modest effect on the risk of breast cancer, but there remain only a handful of genes in which mutation substantially elevates the risk of breast cancer. These include BRCA1, BRCA2, TP53 and PTEN. Whilst breast cancer occurring in patients in Li-Fraumeni and Cowden's syndrome families is of great importance, the more frequent scenario is that of women, or indeed of men, presenting with breast cancer with an underlying germline mutation in BRCA1 or BRCA2. Should these individuals be treated differently because they have had a breast cancer or are at risk of the disease because of a BRCA1 or BRCA2 mutation? In this review, we consider whether BRCA1 or BRCA2 mutation influences the choice of breast screening and breast cancer prevention strategies. Furthermore, for women with an established breast cancer whether their mutation directly influences (1) baseline prognosis, (2) the results of local surgical and radiation therapy, (3) the benefits from adjuvant systemic therapy and finally (4) whether selection or avoidance of particular systemic agents is guided by the presence of a BRCA1 or BRCA2 germline mutation?