title: The incidence of diagnosed autism spectrum disorders in Finland.
abstract: BACKGROUND
  Previous reports indicate an increase in incidence of autism spectrum disorders (ASD).
  
  
  OBJECTIVE
  First, to assess the incidence of diagnosed ASD in children born between 1996 and 1998, based on nationwide inpatient and outpatient register information. Second, to investigate the incidence rate over time of diagnosed ASD and specifically childhood autism, Asperger's syndrome and pervasive developmental disorder (PDD-NOS) in children born between 1987 and 1998.
  
  
  METHODS
  This is population-based cohort study with children born in Finland between 1 January 1987 and 31 December 2005; a total of more than 1.2 million children. Children were identified in the Finnish Hospital Discharge Register, and the reported diagnoses were based on the International Statistical Classification of Diseases (ICD-10, ICD-9).
  
  
  RESULTS
  The annual incidence rate of diagnosed ASD based on inpatient and outpatient register data was 53.7 per 10,000 (95% CI 50.4-57.2). Incidence was 82.6 per 10,000 in boys and 23.6 per 10,000 in girls, yielding a sex ratio (boys:girls) of 3.5:1. We report an eightfold increase in the incidence rates in children of diagnosed ASD and specifically in childhood autism, Asperger's syndrome and PDD-NOS and born between 1987 and 1992 based on inpatient register information.
  
  
  CONCLUSIONS
  Increased awareness of ASD, more precise diagnostic criteria and changes in practice for diagnosing autism may have had a substantial effect on the increased incidence of inpatient treated ASD cases from 1987 to 1992. Between 1992 and 1998, the incidence rate based on inpatient and outpatient service use remained rather stable.
authors.affiliation: Susanna Hinkka-Yli-Salomäki, Department of Child Psychiatry, University of Turku , Turku , Finland.
authors.forename: Susanna
authors.initials: S
authors.lastname: Hinkka-Yli-Salomäki
authors.forename: P Nina
authors.initials: PN
authors.lastname: Banerjee
authors.forename: Mika
authors.initials: M
authors.lastname: Gissler
authors.forename: Katja M
authors.initials: KM
authors.lastname: Lampi
authors.forename: Raija
authors.initials: R
authors.lastname: Vanhala
authors.forename: Alan S
authors.initials: AS
authors.lastname: Brown
authors.forename: André
authors.initials: A
authors.lastname: Sourander
mesh_terms: D000293:Adolescent; D020817:Asperger Syndrome / Q000175:diagnosis / Q000453:epidemiology; D002648:Child; D002659:Child Development Disorders, Pervasive / Q000175:diagnosis / Q000453:epidemiology*; D015331:Cohort Studies; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D007223:Infant; D038801:International Classification of Diseases; D008297:Male; D012042:Registries
keywords: Autism; Autism spectrum disorders; Epidemiology; Incidence; Register study