In the current Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), the most significant difference between Autistic Disorder (Kanner's) and Asperger's syndrome is that a diagnosis of the former includes the observation of "[d]belays or abnormal functioning in at least one of the following areas, with onset prior to age 3 years: (1) social interaction, (2) language as used in social communication, or (3) symbolic or imaginative play, while a diagnosis of Asperger's syndrome observes "no clinically significant delay" in these areas.
The DSM makes no mention of level of intellectual functioning, but the fact that Asperger's autistic's as a group tend to perform better than those with Kanner's autism has produced a popular conception that Asperger's syndrome is synonymous with "higher-functioning autism," or that it is a lesser disorder than autism. There is also a popular but not necessarily true conception that all autistic individuals with a high level of intellectual functioning have Asperger's autism or that both types are merely geek's with a medical label attached. Also, autism has evolved in the public understanding, but the popular identification of autism with relatively severe cases as accurately depicted in Rain Man has encouraged relatives of family members diagnosed in the autistic spectrum to speak of their loved ones as having Asperger's syndrome rather than autism.