The BRCA1 et BRCA2 genes are involved in 2/3 of genetic predisposition with major risk of breast cancer. One or more genes remain to be identified. The CHEK2 gene is a good candidate. The CHEK2 gene mutation 1100delC is associated with a moderate increase of breast cancer risk (RR = 2). CHEK2 is probably one of the genetic factors associated with moderate risk, but however when associated with other variants, it could explain some familial breast cancer and sporadic cancer cases. It seems to be too early to include CHEK2 in genetic counselling at the present time.