Autism presents in a wide degree, from those who are nearly dysfunctional and apparently mentally handicapped to those whose symptoms are mild or remedied enough to appear unexceptional ('normal') to the general public. These autistic persons are often classified as "nerds" or "geeks" by their peers.

"Low-" and "high-functioning":

In terms of both classification and therapy, autistic individuals are often divided into those with an IQ<80 referred to as having "low-functioning autism" (LFA), while those with IQ>80 are referred to as having "high functioning autism" (HFA). Low and high functioning are more generally applied to how well an individual can accomplish activities of daily living, rather than to IQ. The terms low- and high-functioning are controversial and not all autistics accept these labels.

This discrepancy can lead to confusion among service providers who equate IQ with functioning and may refuse to serve high-IQ autistic people who are severely compromised in their ability to perform daily living tasks, or may fail to recognize the intellectual potential of many autistic people who are considered LFA. For example, some professionals refuse to recognize autistics who can speak or write as being autistic at all, because they still think of autism as a communication disorder so severe that no speech or writing is possible.

As a consequence, "high-functioning" autistic persons, and autistic people with a relatively high IQ, are under-diagnosed, thus making the claim that "autism implies retardation" self-fulfilling. The number of people diagnosed with LFA is not rising quite as sharply as HFA, indicating that at least part of the explanation for the apparent rise is probably better diagnostics.

Asperger's and Kanner's syndrome:

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 " delays 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 in these areas a diagnosis of Asperger's observes "no clinically significant delay."

The DSM makes no mention of level of intellectual functioning, but the fact that Asperger's autistics 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 geeks with a medical label attached.

Autism has evolved in the public understanding, but the popular identification of autism with relatively severe cases as accurately presented 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.

As of 2003, psychiatric professionals have been considering redefining Asperger's autism and renaming it as Crypto Sensitivity Syndrome.