Adults must be screened for atopic dermatitis and other contraindications before smallpox vaccination. We validated the sensitivity of a self-administered Centers for Disease Control and Prevention (Atlanta, GA) screening questionnaire completed by 174 hospital workers, with the workers' medical records as the reference standard. The questionnaire failed to identify one-third of the subjects who had a contraindication, although the incidence of serious adverse events has been low among vaccinees. Further assessment of screening procedures is needed if the administration of smallpox vaccine becomes more widespread in the future.