The breast cancer susceptibility gene, BRCA1, was isolated in 1994. Recent investigations into the genetic epidemiology of BRCA1 have revealed an unexpectedly high prevalence of mutations amongst Ashkenazi Jews. Analyses of BRCA1 function have indicated that it may act as an inhibitor of cell proliferation and is necessary for normal development in the mouse. The presence of a motif in BRCA1 characteristic of a family of proteins known as granins, has led to the suggestion that the protein is secreted into the extracellular space. The BRCA2 gene has recently been identified. BRCA2 encodes a large protein of 3418 amino acids without strong homology to any other protein in the database. However, BRCA2 also contains a putative granin motif and a different eight times repeated motif of unknown function. In addition to breast and ovarian cancer, germline BRCA2 mutations probably confer a small risk of a wide range of cancers. Somatic mutations of BRCA2 in sporadic breast and ovarian cancer are very rare. The gene for Cowden syndrome has recently been located and it will now be possible to assess whether it is responsible for the set of families not accounted for by BRCA1 and BRCA2.