Autism is considered a spectrum disorder. According to the National Institute of Child Health & Human Development, a spectrum disorder is "a group of disorders with similar features. One person may have mild symptoms while another may have serious symptoms. But they both have an autism spectrum disorder."  There are three different categories within the autistic spectrum disorders:
- Autistic disorder, sometimes referred to as autism
- Asperger's syndrome
- Pervasive developmental disorder, not otherwise specified
While the term "high functioning autism" (HFA) is often used, there is no formal diagnosis with that name. Experts also disagree with what this term means and use it in different ways. For some, "high functioning" is used for individuals with autism who can integrate in society with minimal support. This use, however, is vague and may mean different things to different people. If your doctor diagnoses you with HFA or uses this term to refer to your child, you may want to ask specifically what he means.
The following are some of the different ways this term is used:
- Children who can clearly meet the diagnostic criteria for autism, such as delayed speech, repetitive behaviors or the lack of eye contact, but have an IQ above 70 are sometimes considered high functioning. Some medical providers may use the diagnosis of pervasive developmental disorder, not otherwise specified, instead of high functioning autism for these individuals.
- One of the classic symptoms of autism is delayed speech. Some medical experts use the term high functioning autism for children or individuals who showed all the classic symptoms of autism early in their childhood but later developed speech and are able to use language meaningfully and clearly communicate with others.
- Another classic autistic symptom is the lack of social interaction. Children with autistic characteristics but have a desire and ability to socially interact with others are sometimes considered high functioning.
- Anyone who doesn't fit "classic autism" but still demonstates autistic behaviors. For example, may use meaningful language, show affection, complete daily tasks but may not like to be touched, doesn't pick up on social cues, doesn't engage in conversation, has consuming special interests and doesn't make eye contact
- HFA can also be used to describe any person with autism who has the ability to live an independent life with very little support. This is a subjective description as each person's idea of minimal support may be different.
HFA is sometimes used interchangeably with Aspeger's syndrome. Often, the development of speech is what separates AS from a diagnosis of autism. If speech is developed at normal ages but there are autistic tendencies or characteristics, AS would be diagnosed, if speech is delayed, then autism would be diagnosed.
Besides language, there is debate as to other areas that may be different between AS and HFA. Some experts argue that AS is autism without any additional learning disability and that individuals who are HFA may have additional learning disabilities. AS is often not diagnosed until a child reaches school age, when social deficits are more apparent, however, HFA can and often is diagnosed earlier. Some children are given a diagnosis of HFA during the pre-school age and then the diagnosis is changed to AS later, as the social deficits become the main symptom.
As we learn and understand more about autism spectrum disorders, this debate will most likely continue. Having an accurate diagnosis is important to determining the course of treatment, however, all of this may end next year, when, and if, the Diagnostic and Statistical Manual (DSM) discontinues the term Asperger's syndrome and instead uses the umbrella term of autism spectrum disorders to include the individuals now diagnosed with AS.
"Autism Spectrum Disorders," Updated 2012, Jan, Melinda Smith, Jeanne Segal and Ted Hutman, Helpguide.org: http://www.helpguide.org/mental/autism_spectrum.htm
 Autism Spectrum Disorders (ASDs), Updated 2011, Nov 15, Staff Writer, National Institute of Child Health & Human Development: http://www.nichd.nih.gov/health/topics/asd.cfm
"Differential Diagnosis in Autism Spectrum Disorders," 2003, Laurie Stephens, The Help Group: http://www.thehelpgroup.org/pdf/guide/Stephens_ASD.pdf "High-functioning Autism and Asperger syndrome: What's the Difference?" Updated 2012, Jan, Staff Writer, The National Autistic Society: http://www.autism.org.uk/en-gb/about-autism/autism-and-asperger-syndrome-an-introduction/high-functioning-autism-and-asperger-syndrome-whats-the-difference.aspx