PURPOSE: We sought to identify factors associated with hepatitis B virus vaccination, including knowledge and attitudes about hepatitis vaccination, and sexual and nonsexual risk behaviors among at-risk homosexual and bisexual men. SUBJECTS AND METHODS: Internet electronic communications were used to collect data from homosexual and bisexual men from the United States, using a 31-item online questionnaire accessible for 1 month. RESULTS: The mean (+/- SD) age of the 336 respondents was 38 +/- 11 years. Nearly 42% (142) reported at least one dose of vaccine; the remainder were completely unvaccinated. About 21% (n = 71) reported having no information about hepatitis. Approximately 72% (242) of respondents reported never using condoms during oral intercourse, and 26% (n = 87) reported using condoms during less than half of their episodes of anal intercourse. In multivariate analysis, variables associated with vaccination were younger age (odds ratio [OR] 0.7 per 10-year increase in age; 95% confidence interval [CI] 0.59 to 0.84, P = 0.002), high level of knowledge about the vaccine (OR 1.4; 95% CI: 1.03 to 1.83, P = 0.007), communication with a health-care provider about hepatitis (OR 1.98; 95% CI 1.31 to 2.98, P = 0.006), and professional training that included hepatitis education (OR 2.77; 95% CI 1.7 to 4.5, P = 0.001). CONCLUSIONS: Our findings underscore the need for health care providers to emphasize vaccine efficacy and safety, and to encourage high-risk patients to receive vaccination, particularly among men at high risk based on sexual and drug use behaviors.