To date, BRGA1 and BRCA2 mutations in breast and/or ovarian patients have not been characterized in the Turkish population. We investigated the presence of BRCA mutations in 53 individuals with a personal and family history of breast andior ovarian cancer, and 52 individuals with a personal history of breast cancer diagnosed below age 50 without additional family history. We have identified 11 mutations (nine BRCA1 and two BRCA2) using combined techniques involving protein truncation test, direct sequencing and heteroduplex analysis. We found eight out of 53 patients (15.1%) with a family history to carry BRCA gene mutations (seven BRCA1 and one BRCA2). Of these, four were found in 43 families presenting only breast cancer histories, and four were found in families presenting ovarian cancer with or without breast cancer. We also demonstrated two BRCA1 and one BRCA2 mutations in three out of 52 (5.8%) early-onset breast cancer cases without additional family history. Three of nine BRCA1 and both BRCA2 mutations detected in this study were not reported previously. These mutations may be specific to the Turkish population. The BRCA1 5382insC mutation, specific to Ashkenazi and Russian populations, was found twice in our study group, representing a possible founder mutation in the Turkish population. (C) 2000 Cancer Research Campaign.