In the research funded by the Japanese Ministry of Health, Labour and Welfare, the prevalence of preschool children with autism spectrum disorder (ASD) was found to have risen to 3-6% in some areas where regional systems of early detection and early support have been established. In this paper, the author discusses the possibility of overdiagnosis and overlooked diagnoses lying behind this high prevalence. The author also discusses introducing social adjustment into the diagnostic criteria and the difference in the range between needs in research and those in clinical support.
 Some of the children diagnosed with ASD at preschool age grow up with remaining symptoms of autism spectrum but with no more need for social support, which the author calls 'autism spectrum without disorder (ASWD)'. Those with ASWD might be regarded as being overdiagnosed, but they might grow up to need some support, and thus will retain a diagnosis of ASD if not supported from their childhood. Although a definitive diagnosis of ASD should be made carefully, it is recommended that children are followed-up in some way once they develop symptoms of autism spectrum.
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