BACKGROUND: The ongoing controversy over the distinction between autistic disorder and Asperger's disorder is important to resolve because of the implications regarding an understanding of the aetiology and prognosis, and the diagnostic and clinical practices relating to these conditions. This paper provides a critical evaluation of current published research evidence. METHOD: Databases, such as PsychINFO and Medline, as well as book chapters, reference lists from relevant articles, and recent editions of key journals were searched for all relevant studies (until 2002) which incorporated participants diagnosed with high-functioning autism and Asperger's disorder using either cluster analysis or comparative approaches to examine similarities and differences between these groups. Keywords used in the searches included autistic disorder, Asperger's disorder, autism, high-functioning autism, and pervasive developmental disorder. RESULTS: On the basis of the available evidence, there seem to be few qualitative differences between autistic disorder and Asperger's disorder. CONCLUSION: There is currently insufficient evidence to establish the validity of Asperger's disorder as a syndrome distinct from high-functioning autism. The findings are consistent with the view that these disorders belong on an autism spectrum.