BACKGROUND: Recent studies have suggested that adult hepatitis B vaccination may be associated with adverse reactions. OBJECTIVE: To further examine the relative risk, percentage association, and statistical significance of arthritic, immunologic, and gastrointestinal adverse reactions reported after adult hepatitis B vaccination compared with control vaccines. DESIGN: The Vaccine Adverse Events Reporting System (VAERS) database was analyzed for the incidence of adverse reactions after adult hepatitis B immunization compared with the incidence of adverse reactions reported to VAERS about vaccine control groups. SETTING: The medical and scientific communities have generally accepted that hepatitis B vaccine, a highly purified, genetically engineered single-antigen vaccine, is a safe vaccine. METHODS: The VAERS database was analyzed from 1997 to 2000 for adverse reactions associated with adult hepatitis B vaccination and from 1991 to 2000 for adverse reactions reported about vaccine control groups. RESULTS: The results showed a statistically significant increase in the incidence of adverse reactions reported after adult hepatitis B vaccination when compared with the incidence of adverse reactions reported to VAERS about control vaccines. CONCLUSIONS: Patients and physicians need to be fully informed of the potential adverse reactions associated with hepatitis B vaccination so that together they can make an informed consent decision about the risk versus the benefit. Patients who may have had an associated adverse reaction to hepatitis B vaccine should be made aware that they may be eligible for compensation from the no-fault Vaccine Compensation Act, administered by the US Court of Claims. TRASFONDO: Estudios recientes sugieren que la vacunación para hepatitis B en adultos podría estar asociada con reacciones adversas.