The study estimated the number of new HIV infections in the United States from 2006 to 2009 using improved methodology based on incidence surveillance data from 16 states and 2 cities. The estimated HIV incidence among individuals aged 13 years and older was 48,600 in 2006, 56,000 in 2007, 47,800 in 2008, and 48,100 in 2009. Overall, HIV incidence remained relatively stable during this period, but there was a significant increase in incidence among young men who have sex with men (MSM) aged 13–29 years, particularly among young black/African American MSM. The study highlights the need for expanded, improved, and targeted prevention efforts to reduce HIV incidence, especially among high-risk populations.The study estimated the number of new HIV infections in the United States from 2006 to 2009 using improved methodology based on incidence surveillance data from 16 states and 2 cities. The estimated HIV incidence among individuals aged 13 years and older was 48,600 in 2006, 56,000 in 2007, 47,800 in 2008, and 48,100 in 2009. Overall, HIV incidence remained relatively stable during this period, but there was a significant increase in incidence among young men who have sex with men (MSM) aged 13–29 years, particularly among young black/African American MSM. The study highlights the need for expanded, improved, and targeted prevention efforts to reduce HIV incidence, especially among high-risk populations.