The Thimerosal and Autism Study is a case-control study conducted in three U.S. managed care organizations (MCOs). Data collection began in 2005 and took three years to complete. In this study, children who were diagnosed with autism were matched with control children. The autism diagnosis of the case samples was confirmed by a standardized clinical assessment protocol. Vaccination histories and information on other potential confounding factors were confirmed by reviewing the medical records for all children. In addition, the mothers of both cases and matched controls were interviewed.