PURPOSE: Most epidemiological and clinical studies on BRCA1/ 2 mutations and the risk of breast cancer have been based on Western cohorts. There have been few such studies for Korean populations. The primary aim of this paper is to report the protocol of a Korean Hereditary Breast Cancer (KOHBRA) study. METHODS: The multi-centers registered in the Korean Breast Cancer Society are participating in the KOHBRA study. The objectives of the KOHBRA study till 2010 is to examine the prevalence of BRCA1/2 mutation and the prevalence of ovarian cancer among the high risk group of hereditary breast cancer patients and their families. This study is a prospective cohort study that recruited 2,250 subjects: 1) who were breast cancer patients with a family history of breast or ovarian cancers, 2) who were patients with a high risk of BRCA1/2 mutations (i.e. early onset, bilateral, male, multiple primary cancers), and 3) who had family members that were BRCA1/2 mutation carriers. The recruiting period will cover the 25th of May 2007 to the 24th of May 2010. Written informed consent is obtained at the time of enrollment. The family history and epidemiological data are obtained by a baseline questionnaire, the anthropometric data is measured and the clinical information is collected by chart-reviews by doctors. BRCA1/2 mutation testing and ovarian cancer screening are done. Blood samples are stored. Follow-up data are collected at 1, 3 and 5 yr after enrollment. RESULTS: Until now, 36 centers have joined the KOHBRA study and they are in the process of Institutional Review Board (IRB) approval. We expect to find the Korean founder mutation and to establish the Korean BRCA risk prediction model. Furthermore, the BRCA carrier cohort established from the KOHBRA study will be the groundwork to participate in an international study. CONCLUSION: The KOHBRA study will provide unique, important data to prove the etiology and natural history of Korean hereditary breast cancer. This study will be continued as genomic and proteomic epidemiological studies and future intervention studies for the prevention of hereditary breast cancer among Koreans.