The incidence of childhood autism and other autistic spectrum disorders (ASDs) in preschool children was determined for two areas of the West Midlands between 1991 and 1996. Children diagnosed before the age of 5 years and residing within the study areas at diagnosis were detected from the records of four child development centres. The incidence rate per 10,000 children per year for the combined areas was 8.3 for all children with ASDs, 3.5 for classical childhood autism (CA), and 4.8 for other ASDs. Rates were similar in both areas, despite differences in social deprivation and proportions of ethnic minorities. While rates for classical CA increased by 18% per year, a much larger increase (55% per year) was seen for 'other ASDs', suggesting that clinicians are becoming increasingly able and/or willing to diagnose ASDs in preschool children.