This paper describes a total population study of Asperger syndrome using a two-stage procedure. All school children in an outer Göteborg borough were screened. Final case selection based on clinical work-up showed a minimum prevalence of 3.6 per 1.000 children (7-16 years of age) using Gillberg and Gillberg's criteria and a male to female ratio of 4:1. Including suspected and possible Asperger syndrome cases, the prevalence rose to 7.1 per 1.000 children and the male:female ratio dropped to 2.3:1. These findings are discussed as they relate to previously published results in the field and to findings obtained using Szatmari et al.'s and ICD-10 draft criteria for the disorder.