* Abbreviations: AAP = : American Academy of Pediatrics • ACIP = : Advisory Committee on Immunization Practices • IPV = : inactivated polio vaccine • FDA = : Food and Drug Administration • DTwP = : diphtheria and tetanus toxoids and whole-cell pertussis vaccine • DTaP = : diphtheria and tetanus toxoids and acellular pertussis vaccine • DTP = : diphtheria, tetanus, and pertussis vaccine • CDC = : Centers for Disease Control and Prevention • NCVIA = : National Childhood Vaccine Injury Act • VICP = : Vaccine Injury Compensation Program • IOM = : Institute of Medicine • OPV = : oral polio vaccine • VIS = : Vaccine Information Statements Concern over vaccine safety has been a major determinant of immunization policy—from passage of the Biologics Control Act in 1902 to the recent American Academy of Pediatrics (AAP) and Advisory Committee on Immunization Practices (ACIP) recommendations for expanded use of inactivated polio (IPV) and acellular pertussis vaccines.1-4 With the availability of new vaccines and vaccination options comes the challenge of how best to communicate these options to patients and their parents. Lessons from the field of risk communication on predictors of risk acceptability and vaccination decision heuristics provide insight into why some parents resist vaccination. This article provides a historical perspective on vaccine adverse events and applies lessons from risk communication research to help physicians improve their ability to discuss vaccine risks. Immunizations have been described as the single most effective health intervention after clean water and sewage disposal,5 and have an extraordinary safety record. However, public policy has long reflected concern for the safety of vaccines and related biologics. In 1902, Congress passed the Biologics Control Act in response to the death of 13 children who had received injections of diphtheria antitoxin contaminated with tetanus toxin.6 This act required biologics to be manufactured in a manner that assured their safety, purity, and potency. Responsibility for these regulations was assigned originally to the Hygienic Laboratory of the Public Health Service, which evolved into the National Institutes of Health. The regulation of biologics including vaccines was transferred to the Food and Drug Administration (FDA) in 1972. The first published accounts of serious adverse events after whole cell pertussis vaccine occurred in 1933 with Madsen's7 report of two deaths within 48 hours of immunization, and in 1948 with the report in Pediatrics by Byers and Moll8 of encephalopathy after diphtheria and tetanus toxoids combined with whole-cell pertussis …