Several different diagnostic sets of criteria exist for Asperger syndrome (AS), but there is no agreement on a gold standard. The aim of this study was to compare four diagnostic sets of criteria for AS: the ICD-10, the DSM-IV, the Gillberg & Gillberg, and the Szatmari criteria. The series consists of 36 children who had been referred to two centers with a tentative diagnosis of AS. The best agreement was between the ICD-10 and the DSM-IV criteria (Kappa coefficient 0.48), and the lowest between the Gillberg & Gillberg and Szatmari criteria (Kappa coefficient -0.21). The poor agreement between these sets of diagnostic criteria compromises the comparability of studies on AS.