Inherited mutations in the genes BRCA1 and BRCA2 are associated with a significantly increased risk of breast cancer, particularly before the age of 50 years, as well as an increased risk of ovarian cancer. Patients with early-onset breast cancer or ovarian cancer at any age with a family history of either disease are at higher risk of carrying a mutation in BRCA1 or BRCA2. Laboratory analysis of these genes can determine whether a patient has inherited an increased risk of breast and ovarian cancer. In the absence of a mutation that has been previously identified in a family member, most tests for hereditary breast-ovarian cancer risk analyze the entire coding sequences of BRCA1 and BRCA2. The gene sequencing process itself can be automated, but the data must be interpreted by an individual with training in molecular diagnostics. Management options generally available to individuals with hereditary susceptibility to breast and ovarian cancer include heightened surveillance, prophylactic surgery, and chemoprevention. The use of genetic techniques to identify women with increased risk of cancer demonstrates the application of recent advances in the understanding of the genetic basis of malignancy to laboratory medicine and clinical care.