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. Those data were reported to CDC through June 2009 from 37 states with mature (in operation since at least January 2005) HIV surveillance systems. This report describes the results of those analyses, which indicated that during 2005-2008, blacks/African Americans were diagnosed with HIV infection more frequently than any other racial/ethnic population. During 2008, black/African American males and females were diagnosed with HIV infection at eight and 19 times the rates for white males and females and two and four times the rates for Hispanic/Latino males and females, respectively. In addition, the number of HIV diagnoses made each year among black/African American males increased during 2005-2008. The reduction of HIV-related health disparities has been identified as one of the three goals in the National HIV/AIDS Strategy. Reducing HIV risk behaviors and increasing access to testing and referral to health care can help eliminate disparities between blacks/African Americans and other racial/ethnic populations in the rates at which HIV infection is diagnosed.