Self-reported hepatitis B virus (HBV) infection status and immunization status were compared with HBV serological markers among 324 young injection drug users (IDUs) and noninjection drug users (NIDUs). The overall validity of self-reported status was poor; 52% claiming to be vaccinated were actually susceptible to HBV. There was no difference in validity of self-reported HBV status between IDUs and NIDUs. Clinicians should adopt a "Don't Ask, Vaccinate" vaccination policy for young drug users.