The clustering of breast cancers in family members has been known since Roman times. This observation has been given added clinical significance with the discovery of a family of breast cancer genes, BRCA1 and BRCA2. The BRCA1 gene is the first adult-onset cancer gene mapped to a single gene locus. Certain inherited mutations in either of these genes greatly increase a patient’s lifetime risk of breast and other cancers. These landmark discoveries are already having an impact on clinical care and have raised ethical, social, and medical issues, many of which are unprecedented. In many ways, the discovery of the genes predated our ability to deal with complex issues surrounding access to testing, informed consent, and interventions. This problem is compounded by the magnitude of the breast cancer epidemic. The cumulative lifetime risk of developing breast cancer for women in the United States is 12.6%, or one in eight women. There are 184,300 new breast cancer cases diagnosed annually in the United States and 44,300 deaths.1