Replication of risk factors from previous studies and a significant risk factor 'dose' effect add to growing evidence that maternal and perinatal factors are low magnitude risk factors for autism. The association between developmental disability and autism risk factors warrants further examination.

Aim: To ascertain the incidence of autism spectrum disorders in Australian children. Setting: New South Wales (NSW) and Western Australia (WA), July 1999 to December 2000. Design: Data were obtained for WA from a prospective register and for NSW by active surveillance. Main outcome measures: Newly recognised cases of autism spectrum disorders (defined as autistic disorder, Asperger disorder and pervasive developmental disorder not otherwise specified [PDD‐NOS]) in children aged 0–14 years; incidence was estimated in 5‐year age bands (0–4 years, 5–9 years, 10–14 years). Results: In WA, 252 children aged 0–14 years were identified with autism spectrum disorder (169 with autistic disorder and 83 with Asperger disorder or PDD‐NOS). Comparable figures in NSW were 532, 400 and 132, respectively. Most children were recognised with autistic disorder before school age (median age, 4 years in WA and 3 years in NSW). Incidence of autistic disorder in the 0–4‐years age group was 5.5 per 10 000 in WA (95% CI, 4.5–6.7) and 4.3 per 10 000 in NSW (95% CI, 3.8–4.8). Incidence was lower in older age groups. The ratio of all autism spectrum disorders to autistic disorder alone was 1.5:1 in WA and 1.3:1 in NSW, and rose with age (1.8:1 and 2.9:1  in 10–14‐year‐olds in WA and NSW, respectively). Conclusions: These are the first reported incidence rates for autism for a large Australian population and are similar to rates reported from the United Kingdom. Ongoing information gathering in WA and repeat active surveillance in NSW will help to monitor any future changes.

Aim:To describe the use of diagnostic labels by clinicians for children with autism spectrum disorders (ASD) and calculate the label-specific and overall agreement between diagnostic labels and Diagnostic and Statistical Manual of Mental Disorders -Fourth Edition (DSM-IV) diagnoses provided by the same clinician. Methods: State-wide active surveillance was used to ascertain children newly recognised with one or more DSM-IV criteria for autistic disorder aged 0-15 years (incident cases) in New South Wales (NSW) between July 1999 and December 2000. Clinicians were asked to supply a diagnostic label and then complete DSM-IV criteria for each child reported. Results: Questionnaires with diagnostic label and DSM-IV criteria were returned for 348 children. The agreement between labels used and diagnosis based on DSM-IV classification system was the highest for autism (97%) and lower for labels of Asperger disorder, pervasive developmental disorder -not otherwise specified or atypical autism (27%). Kappa overall agreement was 0.31. Level of agreement between label and DSM-IV diagnosis was similar for questionnaires completed by multidisciplinary teams, psychiatrists, paediatricians and psychologists working as part of a team. Conclusion: A lack of agreement between the diagnostic labelling used by clinicians and diagnosis based on DSM-IV criteria indicates a lack of consistency in diagnostic communication that is necessary to provide best clinical care, appropriate services and relevant information to parents and carers.