This study was conducted to determine BRCA1 mutations in Vietnamese patients and relatives at high-risk for breast cancer. Materials and methods: The whole coding region of BRCA1 were sequenced in 50 individuals including 26 patients with early-onset disease (diagnosed with breast cancer before 40 years old) or with family history, and 24 predictive cases from 2 high risk families who did not have breast cancer. Results: Here we report a total of 18 BRCA1 sequence alterations, of which two are deleterious mutations (R1751X and 1792X) found in 10 individuals (20%) from families with multiple breast cancer.