Hepatitis B is a well-recognized occupational hazard of health-care workers that can be prevented with vaccination. However, because data on the current epidemiology of hepatitis B virus (HBV) in this population are limited, no consensus exists regarding the requirement for immunization. In 1980-1989, 4,908 exposures of health-care workers to patients' blood and/or other body fluids were reported and evaluated at a general hospital. During this period, 4.8% of patients to whom health-care workers were exposed were positive for hepatitis B surface antigen (HBsAg). In exposed workers, the rate of protective immunity to HBV (measured by antibody to HBsAg) increased from 14% in 1980 to 55% in 1989. Hepatitis B vaccine became available at this hospital in 1983. The increase in antibody to HBsAg was not associated with an increase in antibody to HBV core antigen; this finding suggests that the increase in immunity was primarily vaccine induced. The incidence of reported clinical hepatitis B in health-care workers decreased from 82/100,000 in 1980-1984 to zero in 1985-1989 (odds ratio = 20.06; P = .0012). Thus, in this study, a program of hepatitis B immunization for health-care workers was associated with a significant decline in clinical HBV infection despite continued exposure to patients positive for HBsAg.