The BRCA2 gene on chromosome 13 has been shown to be associated with familial male and female breast cancer. Here we describe a study on BRCA2 in 21 Icelandic families, including 9 with male breast cancer. We have previously reported linkage to the BRCA2 region in an Icelandic male breast cancer family and subsequently found a strong indication of linkage to BRCA2 and the same BRCA2 haplotype in breast cancer cases from 15 additional families, indicating a common origin. We describe a five base-pair deletion in exon 9 of BRCA2 in an affected male from the male breast cancer family. The same mutation occurs in all the families with the shared BRCA2 haplotype indicating a founder effect. Among mutation carriers there are 12 males with breast cancer, which accounts for 40% of all males diagnosed with breast cancer in Iceland over the past 40 years. Three of them have no family history of breast cancer indicating that this mutation may have variable penetrance. The same BRCA2 mutation appears to be associated with different cancer phenotypes in this population including male and female breast cancer, prostate cancer, pancreas cancer and ovarian cancer.