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Background: The estimated number of new HIV infections in the United States reflects the leading edge of the epidemic. Previously, CDC estimated HIV incidence in the United States in 2006 as 56,300 (95% CI: 48,200-64,500). We updated the 2006 estimate and calculated incidence for 2007-2009 using improved methodology Methodology: We estimated incidence using incidence surveillance data from 16 states and 2 cities and a modification of our previously described stratified extrapolation method based on a sample survey approach with multiple imputation, stratification, and extrapolation to account for missing data and heterogeneity of HIV testing behavior among population groups Principal Findings: Estimated HIV incidence among persons aged 13 years and older was 48,600 (95% CI: 42,400-54,700) in 2006, 56,000 (95% CI: 49,100-62,900) in 2007, 47,800 (95% CI: 41,800-53,800) in 2008 and 48,100 (95% CI: 42,200-54,000) in 2009. From 2006 to 2009 incidence did not change significantly overall or among specific race/ethnicity or risk groups. However, there was a 21% (95% CI:1.9%-39.8%; p = 0.017) increase in incidence for people aged 13-29 years, driven by a 34% (95% CI: 8.4%-60.4%) increase in young men who have sex with men (MSM). There was a 48% increase among young black/African American MSM (12.3%-83.0%; p,0.001). Among people aged 13-29, only MSM experienced significant increases in incidence, and among 13-29 year-old MSM, incidence increased significantly among young, black/African American MSM. In 2009, MSM accounted for 61% of new infections, heterosexual contact 27%, injection drug use (IDU) 9%, and MSM/IDU 3%. Conclusions/Significance: Overall, HIV incidence in the United States was relatively stable 2006-2009; however, among young MSM, particularly black/African American MSM, incidence increased. HIV continues to be a major public health burden, disproportionately affecting several populations in the United States, especially MSM and racial and ethnic minorities. Expanded, improved, and targeted prevention is necessary to reduce HIV incidence [ABSTRACT FROM AUTHOR]