The inheritance of mutated version of either BRCA1 or BRCA2 confers a high risk of developing breast cancer. However, only 10-20 % of the breast cancer families carries BRCA mutations, suggesting the presence of other predisposition genes associated with high risk of breast cancer. In our ongoing breast cancer study, we have observed a trend of a decrease of the age of onset from one generation to the next in some breast cancer families. This suggested the potential presence of clinical anticipation, which has been shown to associate with trinucleotide repeat expansions in many diseases. This study aims at identifying putative breast cancer predisposition gene(s), which have undergone intergenerational expansions of trinucleotide repeats during germ line transmission using the Repeat Expansion Detection (RED) technique. DNA from mothers and daughters of breast cancer families has been screened for the presence of trinucleotide expansions. We have started the screening for expansions in (CAG) and (CGG) repeats initially since they are more commonly shown to be associated with anticipation in genetic disorders. Besides using molecular genome scan, with increasing human genome data, we have been using genome databases for identifying candidate trinucleotide repeat containing genes to study their potential involvement with breast cancer. Our approach has the potential to allow the rapid identification of novel breast cancer predisposition genes which will provide obvious benefits for families with breast cancer, as well as the potential for insights into the pathobiology of this disease.