We studied the association of breast cancer with the polymorphic CA repeat in 108 cases of breast cancer and 108 matched controls from Isfahan city of Iran. The most common genotype in controls and patients was homozygous with allele length of 16. Our findings demonstrate that Women with two short CA repeat (< 19) are at a significantly higher risk of breast cancer, at an estimated odds ratio of 1.86. We have also found that women with short alleles (< 19) had much greater risk of developing cancer before the age of 55 (OR, 3.36).