CDC used 2001–2009 data from the National Health Interview Survey to estimate percentages of persons aged 18–64 years who reported ever being tested for HIV in the United States. Data from the National HIV Surveillance System were used to estimate numbers, percentages, and rates of HIV diagnoses, AIDS diagnoses, and late diagnoses of HIV infection (defined as an AIDS diagnosis made ≤12 months from an initial HIV diagnosis) for persons diagnosed with HIV infection during 2001–2008 and reported to CDC through June 2009; these were used to determine populations and regions most affected by HIV and AIDS, late diagnoses, and trends in late diagnoses over time.