Injection drug users (IDUs) are at very high risk for infection with hepatitis B virus (HBV) through multiperson use of injection equipment and through unprotected sexual contact. Although a safe and efficacious vaccine exists for hepatitis B, there are multiple problems in vaccinating IDUs in the United States, including (1) discrimination against drug users by health care providers, (2) the need to reach IDUs before they are exposed to HBV, (3) paying for the vaccinations, and (4) difficulties in completing the 3-injection vaccination series.We compared 2 methods for delivering free hepatitis B vaccination to IDUs: (1) referral by research staff to local health care providers and (2) on-site vaccination at a syringe exchange program.