The American Psychiatric Association's last version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; APA, 1994) identifies within pervasive developmental disorders five subgroups: (a) autistic disorder; (b) Rett's disorder; (c) childhood disintegrative disorder; (d) Asperger's disorder's and (e) pervasive developmental disorder not otherwise specified. However, the diagnosis of the different sub-groups is difficult to establish, particularly between autistic disorder and Asperger's disorder. This article exposes the diagnostic criteria of autism and Asperger's syndrome in order to illustrate the similarities and differences between the two disorders.