Testing for mutations in BRCA1 and BRCA2 can provide important information about breast and ovarian cancer risk to a small but identifiable subgroup of women. Women who test positive for a BRCA1/2 mutation can pursue more aggressive cancer surveillance and prevention regimens. Among families with known mutations, women who test negative may avoid unnecessary interventions. Currently, little is known about the factors associated with the use of clinical BRCA1/2 testing. The objective of this study was to determine the factors associated with decisions about clinical BRCA1/2 testing among women undergoing clinical BRCA1/2 counseling through a retrospective cohort study of women who participated in a university-based clinic offering breast cancer risk assessment, genetic counseling, and BRCA1/2 testing between January 1996 and April 1998. From the 251 eligible women who responded to a follow-up survey, 125 (50%) had undergone or were undergoing BRCA1/2 testing, 86 (34%) had decided not to undergo testing, and 40 (16%) were undecided about testing. After multivariate adjustment, we found that women who chose to undergo BRCA1/2 testing were more likely to have a known familial mutation [odds ratio (OR), 7.46; 95% confidence interval (CI), 0.97-62.16], more likely to be Ashkenazi Jewish (OR, 6.37; 95% CI, 2.68-15.12), more likely to want cancer risk information for family members (OR, 1.93; 95% CI, 0.99-4.14), more likely to want information about ovarian cancer risk (OR, 1.69; 95% CI, 1.18-3.69), and less likely to be concerned about insurance or job discrimination (OR, 0.45; 95% CI, 0.21-0.94). These associations were also found in the subgroup of women with a predicted probability of a BRCA1 mutation of 25%. Our study suggests that approximately half of eligible women choose to undergo clinical BRCA1/2 testing after participating in counseling. Women who have the highest risk of carrying a mutation, and thus the greatest probability of gaining some useful information from the test results, are most likely to undergo testing. Women who undergo testing are also more interested in ovarian cancer risk information and less concerned about job and insurance discrimination.