Breast cancer penetrance to 70 and to 80 years was 68% (95%CI 64.7–71.3%) and 79.5% (95%CI 75.5–83.5%) respectively for BRCA1 and 75% (95%CI 71.7–78.3%) and 88% (95%CI 85.3–91.7%) for BRCA2. Ovarian cancer risk to 70 and to 80 years was 60% (95%CI 65–71%) and 65% (95%CI 75–84%) for BRCA1 and 30% (95%CI 25.5–34.5%) and 37% (95%CI 31.5–42.5%) for BRCA2. These risks were borne out by a prospective study of cancer in the families and genetic testing of unaffected relatives. The gene discussed is BRCA1; the disease is ovarian cancer.