"Cascade testing" refers to the performance of genetic counseling and testing in blood relatives of individuals who have been identified with specific genetic mutations. Testing protocols and other interventions may save lives and improve health and quality of life for these family members. Obstetrician-gynecologists should know who is eligible for cascade testing and should use all available resources to ensure that cascade testing is offered and occurs in a timely manner. Despite the clear health benefits for specific populations and individuals, obstetrician-gynecologists should be aware of the potential barriers to cascade testing and should know which options can help patients overcome those barriers. Such barriers, however, may be overcome with health care provider awareness and participation in local and state initiatives to improve implementation of cascade testing. Resources (available within federal and state agencies, professional societies, and in advocacy and community groups) are critical to the successful implementation of cascade testing. This Committee Opinion focuses specifically on cascade testing and the role of the obstetrician-gynecologist in clinical and public health efforts to increase identification of women with hereditary cancer syndromes.