Recent studies suggest that genetic polymorphisms of the DNA repair genes have been implicated in breast cancer risk. BRCA1 and BRCA2, two breast cancer susceptibility genes, are essential to maintain chromosomal integrity. This is mediated via regulation of RAD51 during homologous recombination. Dinucleotide polymorphism repeats in the 15q14-21, 17q21 and 13q12-13 regions, where the RAD51, BRCA1 and BRCA2 genes are located, respectively, have been evaluated. The polymorphism was determined using the following microsatellite markers: D15S118, D15S214, D15S1006, D17S855, D17S1323, D13S260 and D13S290. Genotypes containing the (CA)(17) or (CA)(19) alleles in the RAD51 region were found to be associated with a decreased breast cancer risk. Genotype containing the (CA)(17) allele in the 13q12-13 region was found to be associated with an increased breast cancer risk. The results indicate that dinucleotide CA repeat polymorphism at RAD51 and BRCA2 gene regions might be associated with genetic susceptibility to breast cancer.