Antibody to hepatitis B core antigen and antibody to hepatitis B surface antigen were measured in serum samples from 825 personnel at St Louis Children's Hospital (702 were possibly at high risk of occupational hepatitis B virus (HBV) exposure and 123 were office personnel); 5.6% had positive findings for both antibodies, 5.6% had findings for antibody to hepatitis B surface antigens alone, and 1.3% had positive findings for antibody to hepatitis B core antigens alone. The group with positive findings for antibody to hepatitis B surface antigens alone did not have traditional risk factors for HBV infection, suggesting that this serologic finding may not be a reliable indicator of past HBV infection. After accounting for the effects of age, sex, and ethnicity, it was found that no occupational group had a significantly increased prevalence of HBV antibodies compared with prevalence in other personnel. In comparison with volunteer blood donors, only physicians older than 40 years of age had an increased HBV antibody prevalence. It is concluded that St Louis Children's Hospital has not been a high-risk environment for HBV exposure in recent years. However, caution is advised in generalizing these conclusions because other children's hospitals may serve a patient population at higher risk of HBV infection. Decisions regarding HBV immunization policy should take into consideration the fact that personnel at different hospitals may face markedly different risks of HBV exposure.