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Up-to-date estimates of the prevalence of hepatitis B virus (HBV) infection, exposure, and immunity are necessary to assess the effectiveness of ongoing programs aimed at preventing HBV transmission.To determine the prevalence and associations of chronic HBV infection, past exposure, and immunity in the United States from 1999 to 2008.Nationally representative, cross-sectional household survey.U.S. civilian, noninstitutionalized population.39 787 participants in the National Health and Nutrition Examination Survey (1999 to 2008) aged 2 years or older.Chronic HBV infection was defined by presence of serum HBV surface antigen and past exposure by serum antibody to hepatitis B core antigen among persons aged 6 years or older. Infant immunity was defined by presence of serum antibody to hepatitis B surface antigen among children aged 2 years.Among persons aged 6 years or older, 0.27% (95% CI, 0.20% to 0.34%) had chronic HBV infection (corresponding to approximately 704 000 persons nationwide), and 4.6% (CI, 4.1% to 5.0%) had been exposed to HBV (approximately 11 993 000 persons). These estimates are lower (P < 0.001) than estimates of HBV infection (0.42%) and exposure (5.1%) in the United States reported from 1988 to 1994. Infection and past exposure were very uncommon among persons aged 6 to 19 years. Children aged 2 years have high rates of immunity (68.6% [CI, 64.1% to 73.2%]). Adults, including those at high risk for infection, have much lower rates of immunity.Incarcerated and homeless persons were not sampled. Categorization of race or ethnicity did not identify high-risk groups, such as persons of Asian and Pacific Islander descent.A cohort of children and adolescents is growing up in the United States with high rates of immunity against HBV and very low rates of infection. Vaccination of high-risk adults should continue to be emphasized.The Veterans Affairs Research Enhancement Award Program.