Breast cancer in African Americans in the US is more aggressive and has a worse outcome than breast cancer in Caucasians. Although the incidence of breast cancer among US whites is higher than among blacks, the mortality rates for blacks are much higher. Breast cancer in blacks is also associated with a more advanced stage at presentation and pathologically aggressive tumors commonly exhibiting estrogen receptor negativity, higher S-phase fractions, and higher numbers of involved lymph nodes. This paper reviews some of the genetic factors that have been shown to be associated with a difference in breast cancer outcome between African Americans and Caucasians in the US such as the BRCA1 and BRCA2 genes, p53 mutations, UGT1A1 gene polymorphisms, and HER-2/neu gene amplifications/overexpression.