The role of germline BRCA1 mutations in hereditary breast and ovarian cancer (HBOC) has been well established in women in Western countries. However, relatively few studies have been carried out in Chinese population. In the present study, we investigated the frequency and spectrum of germline BRCA1 mutations in Chinese HBOC patients, all of whom were from northern part of China. A total of 25 women with HBOC and ten relatives were analyzed. Mutation screening was performed by a combination of denaturing high-performance liquid chromatography and sequencing. Seven protein-truncating mutations were identified. They were 667delG, 3347A --> T, 3478del5, 4255delCT, 1235A --> G, 2064G --> T, and 5589del8. The first four of the mutations were putative ones never reported before. The prevalence of the protein-truncating mutations in this HBOC series was 40.0%, which is similar to that observed in Western hereditary ovarian cancer patients but higher than that reported in Chinese women with sporadic breast and ovarian cancer. Among the ten relatives we analyzed, six shared the same mutations with their affected relatives. No ovarian cancer was detected after 19 months of follow-up. This study showed that BRCA1 mutations play an important role in Northern Chinese HBOC.