Mutations in the BRCA1 and BRCA2 genes predispose women to breast and ovarian cancer. BRCA1 and BRCA2 are 83 and 86 kb long, with coding sequences of 5.7 and 10.2 kb, scattered over 22 and 26 coding exons, respectively. The large majority of the alterations identified in these genes are point mutations and small insertions/deletions. However, an increasing number of large genomic rearrangements are being identified, especially in BRCA1. This review gives a brief overview of the techniques used to screen the BRCA1 and BRCA2 genes for large rearrangements, and describes those for which the breakpoints have been characterized. The principal mechanisms that are thought to lead to their formation, founder effects, and recombination hotspots, are also discussed.