The Korean Hereditary Breast Cancer (KOHBRA) study was established to evaluate the prevalence and spectrum of BRCA1/2 mutations in Korean breast cancer patients at risk for hereditary breast and ovarian cancer. A total of 2953 subjects (2403 index patients and 550 family members of affected carriers) from 36 centers participated in this study between May 2007 and December 2013. All participants received genetic counseling and BRCA genetic testing. In total, 378 mutation carriers among 2403 index patients were identified. The prevalence of BRCA mutations in specific subgroups was as follows: 22.3 % (274/1228) for breast cancer patients with a family history of breast/ovarian cancers, 8.8 % (39/441) for patients with early-onset (<35 years) breast cancer without a family history, 16.3 % (34/209) for patients with bilateral breast cancer, 4.8 % (1/21) for male patients with breast cancer, and 37.5 % (3/8) for patients with both breast and ovarian cancer. From an analysis of the mutation spectrum, 63 BRCA1 and 90 BRCA2 different mutations, including 44 novel mutations, were identified. The c.7480 (p.Arg2494Ter) mutation in BRCA2 (10.1 %) was the most commonly identified in this cohort. The KOHBRA study is the largest cohort to identify BRCA mutation carriers in Asia. The results suggest that the prevalence of BRCA mutations in familial breast cancer patients is similar to that among Western cohorts. However, some single risk factors without family histories (early-onset breast cancer, male breast cancer, or multiple organ cancers) may limit the utility of BRCA gene testing in the Korean population.