OBJECTIVES: We sought to examine trends in hepatitis B virus (HBV) vaccination among high-risk adults and assess the potential effect vaccinated adolescents have on these trends as they age. METHODS: We used data from the National Health Interview Survey 2000, 2002, and 2004 to examine trends in HBV vaccination among high-risk adults aged 18 to 49 years and in age subgroups (18-29, 30-39, and 40-49 years). We investigated temporal differences in vaccination rates for the 18- to 29-year-old cohort with model-based linear contrasts constructed from a logistic regression model with age and survey year as predictors. RESULTS: There was a significant increasing trend in vaccination prevalence across the 3 survey years (32.6%, 35.3%, and 41.4%; trend test, P=.001). We found that respondents aged 18 to 29 years were more likely to be vaccinated in 2004 than in 2000, after adjusting for relevant confounders (odds ratio=1.73; 95% confidence interval=1.14, 2.6); there was no significant increase in vaccination for the other cohorts. CONCLUSIONS: A cohort effect, in which successfully vaccinated adolescents have reached young adulthood, contributes significantly to recent trends showing improved HBV vaccination among high-risk adults.