PURPOSE: Recent discovery of BRCA1 and BRCA2 genes has made it possible to perform presymptomatic diagnosis in hereditary breast/ovarian cancer families. We have previously reported germline mutations of the BRCA1 gene in Korean hereditary breast/ovarian cancer families. In that study two out of 13 families were found to have germline mutations in BRCA1 gene. One was a nonsense mutation in codon 1815, and the other was a frameshift mutation due to 2 base-pair deletion in codon 1701 of BRCA1 gene. This study was intended to identify germline mutations of the BRCA2 gene in Korean breast/ovarian cancer families. MATERIALS AND METHODS: Peripheral blood DNA was obtained from 10 breast cancer patients registered at the Korean Hereditary Tumor Registry with positive family history of breast and/or ovarian cancer. Exons 11 and 27 of the BRCA2 gene(together accounting for 50% of the coding region of the BRCA2 gene) were amplified by polymerase chain reaction(PCR) and screened for mutations by in vitro transcription/translation method. For confirmation of the mutations, automatic sequencing of the PCR products displaying abnormal truncated protein bands was perfomed. RESULT: We identified an abnormal truncated protein in the exon 11 of the BRCA2 gene from a member of hereditary breast cancer family, SNU-B4. Sequencing analysis revealed a 4 bp deletion in codons 1248-49 of the exon 11, resulting in frameshift that led to premature stop codon and truncation of the protein product. CONCLUSION: We have identified a germline mutation from a Korean hereditary breast cancer family. So far only one case of the same mutation has been registered in Database of BRCA2 mutation (BIC) by a commercial genetic diagnosis company, Myriad Genetics, Inc. Identification of the germline mutation in BRCA2 gene should aid in the accurate presymptomatic diagnosis of the at-risk members in this family.