The long-term vaccination has reduced the public awareness of the risk associated with the disease, while increasing the general concerns about the safety of vaccines and their potential risks of adverse reactions. In late 1990s concerns were raised about a possible link between the presence of thimerosal in vaccine and neuro-developmental disorders such as autism in children. In 2001 Bernard postulated a hypothesis that autism is a novel form of mercury poisoning based on a comprehensive review of the literature. Several other studies reported that the mercury concentrations in children with autism were significantly higher than in non-autistic children. There were controversial viewpoints on this link between the government agencies and independent researchers. In 2001 the U.S. FDA declared that all licensed pediatric vaccines that are routinely recommended and are being manufactured for the U.S. market contain no or only trace amounts of thimerosal. In 2004 the situation of pediatric vaccines in Korea is more or less comparable to that in the U.S.. The KFDA and vaccine manufacturers in Korea should be urged to work to reduce or eliminate mercury-containing preservatives in vaccine. Risk communication is more effective when the uncertainty is stated and when the risks are quantified as much as the scientific evidence permits. The benefits and risks of vaccines containing thimerosal should be discussed with parents. The risk of not vaccinating children far outweighs any known risk of exposure to thimerosal-containing vaccines.