Mutations in the BRCA1 gene are associated with an increased risk of breast and ovarian cancer in carrier women. An understanding of behavioral responses to BRCA1 mutation testing by mutation carriers and non-carriers is important to guide the clinical application of this new technology. This study examined the utilization of genetic testing for a BRCA1 mutation in high-risk individuals and the response of tested women with respect to interventions for early cancer detection and prevention. This study assessed the utilization of genetic testing for both men and women in a large kindred and the behavioral responses by women with respect to use of health care interventions during the 2 years following testing. Participants were offered BRCA1 mutation testing. Surveillance behaviors related to breast and ovarian cancer were assessed by computer-assisted telephone interviews at baseline (prior to genetic counseling and testing), 1–2 weeks, 4–6 months, 1 and 2 years after the provision of test results. Mutation carriers, non-carriers, and individuals of unknown mutation status were compared to determine the impact of test results. Utilization of genetic testing for both men and women are reported and, for women, mammography, breast self-exam, clinical breast exam, mastectomy, oophorectomy, transvaginal ultrasound, and CA125 screening were assessed. Of those fully informed of the opportunity for testing, 55% of the women and 52% of the men pursued genetic testing. With respect to mammography for women 40 years and older, 82% of mutation carriers obtained a mammogram in each year following testing compared to 72% of non-carrier women the first year and 67% the second year. This mammography utilization represents a significant increase over baseline for both mutation carriers and non-carriers. Younger carrier women also significantly increased their mammography utilization from baseline. Overall, 29% of the carrier women did not obtain a single mammogram by 2 years post-testing. At 2 years, 83% of the carrier women and 74% of the non-carriers reported adherence to recommendations for breast self-exam and over 80% of carrier women had obtained a clinical breast examination each year following testing. None of the carrier women had obtained a prophylactic mastectomy by 2 years after testing, although 11% were considering this procedure. Of carrier women 25 years of age and older who had at least one intact ovary at the time of testing, 46% of carriers had obtained an oophorectomy 2 years after testing, including 78% of women 40 years of age and older. The majority of carrier women (73%) had discussed their genetic test results with a medical doctor or health care provider. Our results indicate utilization of genetic testing by a majority of high-risk individuals who received information about testing. Both carriers and non-carriers increased their utilization of mammography and breast self-exam following testing. Oophorectomy was obtained by a large proportion of carrier women in contrast to mastectomy which was not utilized within the first 2 years following testing. © 2003 Wiley-Liss, Inc.