The objective of this study was to establish rates of diagnosed autism spectrum disorders (ASDs) in a circumscribed geographical region. The total population born in 1977–1994, living in Göteborg Sweden in 2001, was screened for ASD in registers of the Child Neuropsychiatry Clinic. The minimum registered rate of autistic disorder was 20.5 in 10,000. Other ASDs were 32.9 in 10,000, including 9.2 in 10,000 with Asperger syndrome. Males predominated. In the youngest group (7–12 years), 1.23% had a registered diagnosis of ASD. There was an increase in the rate of diagnosed registered ASD over time; the cause was not determined. The increase tended to level off in the younger age cohort, perhaps due to Asperger syndrome cases missed in screening.