For parents who still need convincing, a Canadian study once more demonstrates that thimerosal in vaccines is not to blame for a rising incidence of autism. To the contrary: A study published in Pediatrics (2006;118:139) of nearly 28,000 children born between 1987 and 1998 found that the prevalence of pervasive developmental disorders was greater after thimerosal was completely eliminated from vaccines in Canada than when the preservative was still in use. The perceived connection did have regrettable side effects, however: The rate of measles-mumps-rubella (MMR) immunization in Canada declined, putting more children at risk of infectious disease, and some children with autism were exposed to untested, potentially dangerous chelation therapy.