In today's Lancet, Gillian Baird and colleagues 1 Baird G Simonoff E Pickles A et al. Prevalence of disorders of the autism spectrum in a population cohort of children in South Thames: the Special Needs and Autism Project (SNAP). Lancet. 2006; 368: 210-215 Summary Full Text Full Text PDF PubMed Scopus (1422) Google Scholar report a prevalence of pervasive developmental disorders or autism spectrum disorders of 116·1 per 10 000, much higher than previously thought. The researchers base these findings on a total population cohort of 56 946 children aged 9–10 years in 12 districts in southeast Thames, UK, with ICD-10 criteria. 2 WHOThe ICD-10 classification of mental and behavioural disorders: diagnostic criteria for research. World Health Organization, Geneva1993 Google Scholar For subtypes, the prevalence was 38·9 per 10 000 for childhood autism and 77·2 per 10 000 for other pervasive developmental disorders. Nearly 60% of pervasive development disorders as a whole was atypical autism in accordance with recent UK 3 Chakrabarti S Fombonne E Pervasive developmental disorders in preschool children. JAMA. 2001; 285: 3093-3099 Crossref PubMed Scopus (826) Google Scholar and Swedish 4 Gillberg C Cederlund M Lamberg K Zeijlon L Brief report: “the autism epidemic”: the registered prevalence of autism in a Swedish urban area. J Autism Dev Disord. 2006; 36: 429-435 Crossref PubMed Scopus (142) Google Scholar studies, which reported that about one half of pervasive developmental disorders was a not otherwise specified subtype, a DSM-IV equivalent of atypical autism. 5 American Psychiatric AssociationDiagnostic and statistical manual of mental disorders. 4th edn (DSM-IV). APA, Washington, DC1994 Google Scholar Baird and colleagues did not give the prevalence of the other three subtypes (ie, Rett's syndrome, childhood disintegrative disorder, and Asperger's syndrome), because they found no cases of the first two. The researchers identified seven cases who met Asperger's syndrome criteria, but classified these cases as childhood autism because the seven cases also satisfied childhood autism criteria. Prevalence of disorders of the autism spectrum in a population cohort of children in South Thames: the Special Needs and Autism Project (SNAP)Prevalence of autism and related ASDs is substantially greater than previously recognised. Whether the increase is due to better ascertainment, broadening diagnostic criteria, or increased incidence is unclear. Services in health, education, and social care will need to recognise the needs of children with some form of ASD, who constitute 1% of the child population. Full-Text PDF