A mutational screen consisting of the most common mutations, 4446C>T and 2953delGTAinsC in BRCA1 and, 6085G>T and 8765delAG in BRCA2, and 3398delAAAAG accounted for 62 of 74 (84%) mutation-positive French Canadian families with at least three cases of breast cancer (diagnosed before 66 years of age) and/or ovarian cancer. Here, BRCA2 is linked to breast carcinoma.