Blacks/African Americans have been affected disproportionately by human immunodeficiency virus (HIV) infection since early in the epidemic. Despite representing a smaller proportion (13.6%) of the U.S. population, blacks/African Americans accounted for half of the HIV diagnoses in adolescents and adults in 37 states during 2005—2008. Data from the National HIV Surveillance System were used to estimate numbers, percentages, and rates of HIV diagnoses in blacks/African Americans during 2005–2008.