Several genes are associated with hereditary susceptibility to breast cancer. Most notably these include BRCA1 and BRCA2; however, other less common gene mutations which confer elevated breast cancer risk are associated with Cowden syndrome, Li-Fraumeni syndrome, Peutz-Jeghers syndrome, ataxia-telangiectasia heterozygosity and hereditary diffuse gastric cancer. In this article we highlight the genetic epidemiology, gene function, genotype-phenotype correlations, cancer risks and clinicopathologic findings for the cancer susceptibility genes related to these syndromes. We also examine genes, such as CHEK2, which confer a lower penetrance for breast cancer in comparison to these highly penetrant genes.