Autism was first described by Dr. Leo Kanner in 1943.(5) Surveys to find the prevalence of autism started in the mid-1960s in England.(6) Diagnostic criteria for autism and related developmental disabilities came out in 1980, (7,8) and they have been revised several times. Thus, one challenge in getting an accurate count of people with autism has been a changing, more inclusive definition, to consider autism as a spectrum of disorders.(9,10) Another challenge is that the United States has not had a population-based system to track the full range of ASDs over time. And the fact that autism and related disorders are diagnosed by behavioral observation of development makes describing the population of people with ASDs challenging, especially when the criteria for defining ASDs have changed over time.