In the current study, we have assessed linkage disequilibrium and haplotype diversity within high and moderate penetrance breast cancer susceptibility genes in the Tunisian population through the analysis of 387 SNPs identified in BRCA1, BRCA2, STK11, PTEN, TP53, ATM, BRIP1, CHEK2 and PALB2 genes. The gene discussed is CHEK2; the disease is breast cancer.