Hepatitis B virus (HBV) infection is common among injection drug users (IDU). Younger IDU, however, may be less susceptible to infection due to the implementation of public health interventions, such as universal immunization programs and syringe exchange programs. To investigate the current epidemiology of HBV infection and control among a new generation of drug users in the United States, we conducted interviews and examined HBV serologic markers in a cross-section of street-recruited IDU under age 30 in San Francisco, CA. Of the 831 persons studied, 21% showed serologic evidence of current or past infection; 22% had isolated antibodies to hepatitis B surface antigen consistent with vaccine-mediated immunity; and 56% had no HBV markers. In multivariate analyses, HBV infection was associated with drug use behaviour in heterosexual males; sexual behaviour in males who have sex with males; and both drug use and sexual behaviour in females. Vaccine-mediated immunity was independently associated with female sex and younger age. In conclusion, HBV transmission persists among young IDU in San Francisco. Few young injectors show evidence of successful immunization and the majority remains susceptible to disease. Until the broad effects of universal vaccination are seen, targeted and innovative approaches to immunizing young IDU in the US are needed to prevent a substantial number of new HBV infections.