If you have recently started researching autism, you have probably come across articles listing five distinct "types" of autism — Asperger's syndrome, Rett syndrome, childhood disintegrative disorder, Kanner's syndrome, and PDD-NOS. The problem is that this framework has been outdated since 2013. The American Psychiatric Association's DSM-5 merged most of these separate diagnoses into a single category: Autism Spectrum Disorder (ASD). Understanding why that change happened — and what it means for your child's diagnosis and treatment — is more useful than memorizing labels that clinicians no longer use.

This guide explains both the historical categories (because you will still encounter them) and the current diagnostic framework, so you can navigate evaluations, treatment plans, and conversations with providers from an informed position.

TLDR: The DSM-5 (2013) consolidated autistic disorder, Asperger's syndrome, PDD-NOS, and childhood disintegrative disorder into one diagnosis: Autism Spectrum Disorder (ASD). Rett syndrome was removed entirely because it has a known genetic cause (MECP2 mutation). ASD is now classified by three support levels rather than separate categories. The old labels still appear in research and conversation, but clinicians diagnose using the unified ASD criteria with severity specifiers. What matters most for your child is not the label — it is the individualized support plan.

The idea that autism comes in five neat categories was always a simplification. Under the DSM-IV (published in 1994), autism-related conditions were grouped under "Pervasive Developmental Disorders" and divided into separate diagnoses: autistic disorder, Asperger's disorder, PDD-NOS, childhood disintegrative disorder, and Rett syndrome. But clinicians quickly found that the boundaries between these categories were blurry and inconsistent. Two children with nearly identical symptoms could receive different diagnoses depending on which clinician they saw, what criteria were emphasized, and when the evaluation took place.

According to a review published in Current Opinion in Psychiatry , by the time the DSM-5 was being developed, 90% of publications in the field had already shifted to using "autism spectrum disorder" instead of the separate category names. The science had moved ahead of the manual. When the DSM-5 was published in 2013, it caught up by collapsing autistic disorder, Asperger's, PDD-NOS, and childhood disintegrative disorder into a single diagnosis — Autism Spectrum Disorder — and removing Rett syndrome from the autism category entirely.

This matters for parents because the old labels still circulate widely online, in older research, and sometimes even in casual conversation among providers. If someone tells you your child has "Asperger's" or "PDD-NOS," that language may reflect the evaluator's habits or regional conventions, but the official diagnosis in their medical record should read Autism Spectrum Disorder with a severity level.

Even though these categories are no longer used for diagnosis, understanding them helps you make sense of older resources, research studies, and conversations with people who received their diagnosis before 2013.

First described by Leo Kanner in 1943, this was the "classic" autism diagnosis. It involved significant difficulties with social interaction and communication, restricted and repetitive behaviors, and symptoms that appeared before age three. Children diagnosed with autistic disorder typically had more pronounced challenges across all areas — social engagement, verbal communication, and behavioral flexibility. Many also had co-occurring intellectual disability, though not all. Under the current DSM-5 framework, individuals who would have received this diagnosis now fall under ASD, most often at Level 2 or Level 3, depending on their support needs.

Named after Hans Asperger, who published his observations in 1944, Asperger's syndrome described individuals with average or above-average intelligence who had strong verbal skills but struggled significantly with social communication, reading nonverbal cues, and navigating unwritten social rules. People with Asperger's often developed intense, focused interests in specific subjects and preferred routines and predictability. The key distinction from autistic disorder was the absence of clinically significant language delays — children with Asperger's typically hit early language milestones on time or even early.

The elimination of Asperger's as a separate diagnosis in the DSM-5 was one of the most debated changes. Many people who received this diagnosis feel a strong connection to the label as part of their identity. Clinically, the challenge was that the boundary between Asperger's and "high-functioning autism" was nearly impossible to draw reliably. Under the current framework, these individuals would generally be diagnosed with ASD Level 1 — "requiring support."

PDD-NOS was essentially a catch-all diagnosis for children who showed some but not all features of autistic disorder or Asperger's syndrome. A child might have significant social communication challenges but not enough repetitive behaviors to meet criteria for autistic disorder, or they might have symptoms that emerged later than age three. This diagnosis was useful for ensuring children received services, but it was also the least consistent — diagnostic agreement between evaluators was particularly low for PDD-NOS compared to autistic disorder.

Under the DSM-5, many individuals who would have been diagnosed with PDD-NOS now receive an ASD diagnosis. Some who had milder presentations may instead be evaluated for Social (Pragmatic) Communication Disorder, a new category created in the DSM-5 for individuals who have social communication difficulties but do not show restricted and repetitive behaviors.

CDD was the rarest of the five categories. It described children who developed typically for at least two years — hitting all expected milestones in language, social skills, and motor abilities — and then experienced a dramatic regression, losing previously acquired skills in at least two areas. This regression usually occurred between ages two and four and was often accompanied by a seizure disorder. CDD was considered the most severe condition on the spectrum, and the regression was more profound than what is sometimes seen in other forms of autism.

In the DSM-5, CDD was absorbed into the ASD diagnosis. Clinicians now note whether the individual experienced a loss of established skills as part of the diagnostic evaluation, and individuals with this pattern would typically be diagnosed at ASD Level 3 — "requiring very substantial support."

Rett syndrome was unique among the five categories because it has a known genetic cause — mutations in the MECP2 gene on the X chromosome. It overwhelmingly affects girls (boys with the mutation rarely survive to birth) and follows a distinct pattern: apparently typical development for the first six to eighteen months, followed by regression in motor skills, loss of purposeful hand use, development of repetitive hand-wringing movements, and slowed head growth.

The DSM-5 removed Rett syndrome from the autism classification entirely. As researchers explained , the rationale was that the DSM classifies conditions by behavior, not by genetic cause, and Rett syndrome now has a clear genetic basis that distinguishes it from behaviorally defined ASD. However, this removal was controversial. Many girls with Rett syndrome do meet diagnostic criteria for ASD during the regression phase, and some continue to show autistic features throughout their lives. Under the current system, an individual can carry dual diagnoses of Rett syndrome and ASD if they meet criteria for both.

Instead of five separate categories, the DSM-5 uses a single diagnosis of Autism Spectrum Disorder defined by two core areas of difficulty, as outlined by the Children's Hospital of Philadelphia.

Persistent deficits in social communication and social interaction. This includes difficulty with social-emotional reciprocity (back-and-forth conversation, sharing interests, understanding emotions), challenges with nonverbal communication (eye contact, facial expressions, body language), and trouble developing, maintaining, and understanding relationships appropriate to their developmental level.

Restricted, repetitive patterns of behavior, interests, or activities. This includes stereotyped or repetitive motor movements, speech, or use of objects; insistence on sameness and rigid adherence to routines; highly restricted interests with unusual intensity or focus; and hyper- or hypo-reactivity to sensory input.

For a diagnosis, an individual must show deficits in all three areas of social communication AND at least two of the four types of restricted, repetitive behaviors. Symptoms must be present from early childhood (though they may not become fully apparent until social demands exceed the individual's capacities) and must cause clinically significant impairment.

Rather than assigning a "type," the DSM-5 specifies a level of support needed. These levels are assessed separately for social communication and for restricted, repetitive behaviors.

Level 1 — "Requiring Support." The individual has noticeable difficulties with social communication that cause problems without support. They may have trouble initiating social interactions, show atypical or unsuccessful responses to social overtures, or appear to have decreased interest in social interactions. Inflexibility of behavior causes significant interference with functioning in one or more contexts. This level roughly corresponds to what was previously called Asperger's syndrome or mild PDD-NOS.

Level 2 — "Requiring Substantial Support." Marked deficits in verbal and nonverbal social communication are apparent even with supports in place. Social initiations are limited, and responses to social overtures from others are reduced or atypical. Inflexibility of behavior, difficulty coping with change, and restricted or repetitive behaviors appear frequently enough to be obvious to a casual observer. Distress or difficulty changing focus or action is evident.

Level 3 — "Requiring Very Substantial Support." Severe deficits in verbal and nonverbal social communication cause severe impairments in functioning. Very limited initiation of social interactions and minimal response to social overtures from others. Inflexibility of behavior, extreme difficulty coping with change, and restricted or repetitive behaviors markedly interfere with functioning in all areas. Great distress or difficulty changing focus or action.

It is important to understand that these levels are not permanent. A child diagnosed at Level 3 may progress to Level 2 with effective early intervention. A child at Level 1 may need more support during stressful transitions like starting school. The levels describe current support needs, not lifetime potential.

The shift from categories to a spectrum model has practical implications for families.

Diagnosis is more consistent. Under the old system, the same child could receive different diagnoses from different clinicians. The unified criteria reduce that variability, which means more reliable access to services.

Support is based on individual needs, not labels. Rather than fitting your child into a box labeled "Asperger's" or "PDD-NOS," the current system asks: What specific areas of support does this individual need, and how much support is required? This approach leads to more personalized treatment plans.

The severity levels can change. Unlike the old categories, which felt permanent, the DSM-5 levels are explicitly tied to current functioning. This means your child's level of support can be reassessed as they develop and as interventions take effect.

Early intervention is easier to access. Under the old system, some children who fell into the "milder" categories like PDD-NOS were denied services. The unified ASD diagnosis, combined with a support level, makes it clearer that even Level 1 individuals require support — and are entitled to receive it.

If your child is being evaluated for autism, or if you are seeking a re-evaluation, these questions can help you get the most useful information from the process. What specific areas of social communication are affected? What restricted or repetitive behaviors have been observed? What support level is being recommended, and what does that mean practically? Are there co-occurring conditions (anxiety, ADHD, sensory processing differences) that should be addressed? What does the recommended treatment plan look like in the first 90 days? Will a Board Certified Behavior Analyst (BCBA) be supervising therapy? How frequently will progress be reassessed, and how will the support level be reviewed over time?

Asperger's syndrome is no longer an official diagnosis in the DSM-5. Individuals who would have previously received this diagnosis now receive a diagnosis of Autism Spectrum Disorder Level 1. However, many people continue to use the term Asperger's in casual and community contexts, and some countries' diagnostic systems (like the ICD-10, which was used until 2022) retained the category longer than the DSM did.

Yes. While Rett syndrome was removed from the autism category in the DSM-5, individuals with Rett syndrome who also meet DSM-5 criteria for Autism Spectrum Disorder can receive both diagnoses. The dual diagnosis would be noted as "Autism Spectrum Disorder associated with Rett syndrome" or "associated with MECP2 mutations."

The DSM-5 states that individuals with a well-established DSM-IV diagnosis of autistic disorder, Asperger's disorder, or PDD-NOS should be given the diagnosis of Autism Spectrum Disorder. No re-evaluation is required for this reclassification, though a new evaluation can be helpful for determining the current support level and updating treatment plans.

Support levels influence treatment planning and can affect service eligibility, but they are not the sole factor. A comprehensive evaluation that documents specific functional limitations, co-occurring conditions, and support needs provides the strongest basis for accessing services. Work with your child's clinical team and, if necessary, an advocate to ensure your child's evaluation fully captures their support requirements.

Absolutely. Support levels reflect current functioning, not permanent ability. Many children make significant progress with early, intensive intervention — particularly ABA therapy, speech therapy, and occupational therapy — and may require less support over time. Conversely, support needs can increase during developmental transitions, stressful periods, or when environmental demands change.

Many health content websites produce articles about the "five types of autism" because it is a commonly searched term. The information is not wrong historically, but it is outdated for diagnostic purposes. The DSM-5 has been the diagnostic standard in the United States since 2013, and the ICD-11 (adopted internationally in 2022) similarly uses a unified Autism Spectrum Disorder category.

At Treetop ABA, we know that every child on the spectrum has a unique profile of strengths, challenges, and support needs — regardless of what label they came in with. Every treatment plan starts with a comprehensive assessment, including a Functional Behavior Assessment conducted by a Board Certified Behavior Analyst, to understand your child's specific needs and build an individualized program. If your child has recently been diagnosed or you are seeking an evaluation, a free consultation can help you understand what support looks like for your family.

Autism Speaks — Autism Diagnostic Criteria: DSM-5

Children's Hospital of Philadelphia — Diagnostic Criteria for Autism Spectrum Disorder in the DSM-5

Current Opinion in Psychiatry — Update on Diagnostic Classification in Autism

Frontiers in Psychiatry — Autism Spectrum Disorder Versus Autism Spectrum Disorders: Terminology, Concepts, and Clinical Practice

The Transmitter — Reclassification of Rett Syndrome Diagnosis Stirs Concerns

American Psychiatric Association — Highlights of Changes from DSM-IV-TR to DSM-5