What Are the Different Types of Autism?

Autism is a "spectrum disorder," meaning that people with autism may have a wide range of mild, moderate, or severe symptoms. But do all people with an autism spectrum diagnosis have the same disorder, no matter what their symptoms?

How Autism Diagnoses Have Changed

From 1994 to May 2013, the autism spectrum was represented by five autism spectrum diagnoses in the fourth version of the official Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). They included Asperger's syndrome, pervasive developmental disorder—not otherwise specified (PDD-NOS), autistic disorder, childhood disintegrative syndrome, and Rett syndrome.

Because there was overlap among the diagnoses, practitioners (as well as teachers and therapists) sometimes used more general terms like "severe autism," "mild autism," and "high-functioning autism."

These terms, however, aren't true diagnoses at all; they're just descriptions. And while they were intended to help parents and teachers better understand where a child fell on the autism spectrum, each practitioner may have had their own idea of what "mild" or "severe" might look like.

Autism Spectrum Disorder Debuts

In 2013, the fifth version of the Diagnostic Manual (DSM-5) was published. In the DSM-5, there is just one diagnosis for all variations of autism, callled "autism spectrum disorder" (ASD). 

Everyone with symptoms of autism is given a diagnosis of autism spectrum disorder. Within that diagnosis are three levels. Those with Level 1 are the highest functioning, and those with Level 3 are considered severely impaired.

Doctors and other practitioners still use the older terms sometimes, as they are more descriptive than, for example, "Level 2 autism spectrum disorder." They may use the older terms informally, and use the new definitions for billing code purposes.

What Is Asperger's Syndrome?

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Asperger's syndrome describes individuals at the highest-functioning end of the autism spectrum. The term—and the diagnosis—was removed from the diagnostic manual in 2013, but virtually everyone in the autism community continues to use it because of its usefulness in describing a very specific group of people.

People with Asperger's syndrome generally develop spoken language in the same way as typically developing children but have a tough time with social communication. These difficulties become more obvious as they get older and social expectations increase.

Because people with Asperger's syndrome are often very intelligent (but "quirky") the disorder is sometimes nicknamed "geek syndrome" or "little professor syndrome."

Key points about Asperger's syndrome:

  • Asperger's syndrome is no longer a valid diagnosis, per the DSM-V.
  • Asperger's syndrome was and is still often used to describe people with "high-functioning" autism.
  • Most people with the symptoms of Asperger's syndrome are of normal or above normal intelligence with strong verbal skills and significant difficulties with social communication.
  • Many people with Asperger's syndrome have significant sensory challenges.
  • People with symptoms of Asperger's syndrome are now given a diagnosis of Level 1 autism spectrum disorder.

What Is Pervasive Developmental Disorder?

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Pervasive developmental disorder is a term that, between 1994 and 2013, meant exactly the same thing as autism spectrum disorder. If your child was diagnosed before 2013 you may have heard this term from an evaluator or doctor, but it is no longer in general use.

Key points about pervasive developmental disorder:

  • The term pervasive developmental disorder is no longer in general use.
  • The term was synonymous with autism spectrum disorder.
  • People with PDD have a wide range of developmental differences which can be mild or severe.

What Is Mild Autism?

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The term mild autism is not an official diagnosis. It's simply a more descriptive term than Asperger's syndrome or autism. Generally speaking, when people use the term mild autism they are referring to individuals whose symptoms fit an autism spectrum diagnosis, but who have strong verbal skills and few behavioral issues.

Those individuals may, however, have significant problems with social communication. They may also have problems coping with too much sensory input, such as loud noises or bright lights.

Key points about mild autism:

  • Mild autism is essentially similar to or identical to Asperger's syndrome.
  • Symptoms of mild autism may be difficult to recognize until the person is under stress or coping with complex social situations.
  • Most people with mild autism are now considered to have Level 1 autism spectrum disorder.

What Is High Functioning Autism?

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Like "mild" autism, high functioning autism (sometimes shortened to HFA) is a commonly used term. At one point (before 2013), the term was used to distinguish autism from Asperger's syndrome.

The official distinction made by practitioners before 2013 was that people with HFA had or have speech delays, while people with Asperger's syndrome have normal speech development. Of course, these days there is no Asperger's syndrome, making the distinction moot.

What Is PDD-NOS?

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Pervasive developmental disorder not otherwise specified is a mouthful of words that, until 2013, were used to describe individuals who didn't fully fit the criteria for other specific diagnoses but were nevertheless autistic.

Because there is no easy way to define the symptoms of PDD-NOS, which may range from very mild to very severe, the diagnostic category no longer exists, though a new diagnosis, social communication disorder, may become a similar "catchall" category. 

Key points about PDD-NOS:

  • As of 2013, PDD-NOS is no longer a valid diagnosis.
  • PDD-NOS was a catchall for disorders with autism-like symptoms that didn't fit the full criteria for autism.
  • People with PDD-NOS could have mild or severe symptoms.
  • Those people who were diagnosed with PDD-NOS prior to the DSM-5 will now have an autism spectrum diagnosis and may be diagnosed at level 1, 2, or 3 depending on the severity of symptoms.

What Is Severe Autism?

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Severe autism is not an official diagnosis; instead, it is a descriptive term along with profound autism, low functioning autism, and classic autism. People with "severe autism" are often non-verbal and intellectually disabled, and may have very challenging behaviors.

Key points about severe autism:

  • Severe autism is usually diagnosed as level 3 autism spectrum disorder.
  • Severe autism is extremely challenging and may include aggression and other difficult behaviors.
  • Most people with severe autism never gain meaningful use of spoken language.
  • Some people with symptoms of severe autism do gain the ability to communicate through signs, picture boards, or other means.

What Is Rett Syndrome?

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Rett syndrome is a genetic disorder that primarily affects girls. It is the only one of the former autism spectrum disorders that can be diagnosed medically (so far). As of May 2013, it is no longer considered to be on the autism spectrum.

Children with Rett syndrome develop physical symptoms, such as seizures, as well as the hallmark social communication challenges of autism. In addition, Rett syndrome can also profoundly impair a child's ability to use their hands usefully.

Key points about Rett syndrome:

  • Rett syndrome is no longer part of the autism spectrum.
  • Rett syndrome is a genetic disorder with physical symptoms such as seizures, and is therefore a medical diagnosis.
  • Rett syndrome primarily impacts girls, and only rarely boys.
  • Symptoms of Rett syndrome include social communication challenges and the loss of purposeful use of one's hands.

What Is the Broad Autism Phenotype?

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The broad autism phenotype includes people who have what might be called a "touch" of autism. This is sometimes described as having "shadow symptoms." These sub-clinical symptoms can include social awkwardness, anxiety, a preference for sameness and routine, and an unusual degree of discomfort around bright lights, loud noise, and other sensory "assaults."

Such mild symptoms, which are recognizable but which do not significantly impair daily functioning, are common among family members of people with full-blown autism. Is this really autism? Or just a personality type? As with many issues related to autism, it depends on who you ask.

Either way, it is often helpful for people with such symptoms to seek help with building social communication skills and coping with sensory challenges.

Key points about broad autism phenotype:

  • There is a broad autism phenotype which includes people with milder autism-like symptoms.
  • Many people with such symptoms have children or other relatives on the autism spectrum.
  • Many of the treatments available for autism can be helpful for people with milder versions of the same symptoms.
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Article Sources
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  3. Topal Z, Demir samurcu N, Taskiran S, Tufan AE, Semerci B. Social communication disorder: a narrative review on current insights. Neuropsychiatr Dis Treat. 2018;14:2039-2046. doi:10.2147/NDT.S121124

  4. Kyle SM, Vashi N, Justice MJ. Rett syndrome: a neurological disorder with metabolic components. Open Biol. 2018;8(2). doi:10.1098/rsob.170216

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