Autism spectrum disorder (ASD) is now a single diagnosis, but it wasn’t always. Before 2013, what we call “autism” was split into four separate diagnoses, each with its own label and criteria. Today, those former subtypes have been folded into one umbrella diagnosis with three levels of support needs. About 1 in 31 children (3.2%) in the United States are identified with ASD, based on 2022 surveillance data from the CDC.
The Four Former Subtypes
Until the DSM-5 (the diagnostic manual used by mental health professionals) was published in 2013, autism was diagnosed as one of four distinct conditions: autistic disorder, Asperger’s disorder, childhood disintegrative disorder, and pervasive developmental disorder not otherwise specified (PDD-NOS). Each had different criteria, and getting the “right” label often depended on which clinician you saw. The DSM-5 merged all four into the single category of autism spectrum disorder, recognizing that these conditions share the same core features but vary widely in severity.
Understanding the old subtypes still matters. Many adults were diagnosed under the previous system and still identify with those labels. And clinicians sometimes reference them informally to communicate a person’s profile quickly.
Autistic Disorder
This was what most people meant when they said “autism” before 2013. It required clear difficulties in social interaction, communication, and the presence of repetitive or restricted behaviors, all appearing before age 3. Children diagnosed with autistic disorder often had delayed speech, limited eye contact, and strong preferences for routines. The diagnosis covered a wide range of functioning, from children who were nonverbal to those with fluent speech but significant social challenges.
Asperger’s Syndrome
Asperger’s was distinguished from autistic disorder primarily by the absence of language and cognitive delays. Children with Asperger’s typically hit early language milestones on time and had average or above-average intelligence, but they struggled to use language socially. They might speak fluently yet miss sarcasm, talk at length about a narrow interest without reading the listener’s body language, or have difficulty making and keeping friends. Some providers today still use the term informally, though the official equivalent is now “ASD without intellectual or language impairment.”
PDD-NOS
Pervasive developmental disorder not otherwise specified was essentially the “doesn’t quite fit” category. It applied when a person had significant social difficulties paired with either communication problems or repetitive behaviors, but didn’t meet the full criteria for autistic disorder or Asperger’s. Someone might have had severe social deficits but no restricted or repetitive behaviors, or their symptoms appeared later than the typical age cutoff. The Kennedy Krieger Institute described it as “subthreshold autism,” a diagnosis for people with an autistic profile that was either milder in some areas or atypical in its presentation. PDD-NOS was one of the most commonly assigned diagnoses in the old system, partly because clinicians used it as a catch-all when they were uncertain.
Childhood Disintegrative Disorder
This was the rarest of the four. Children with childhood disintegrative disorder (also called Heller’s syndrome) developed normally for at least two years, sometimes up to age 3 or 4, and then lost skills they had already gained. The regression typically happened between ages 3 and 4 but could occur anytime before age 10. To qualify for the diagnosis, a child had to lose previously acquired abilities in at least two areas: expressive or receptive language, social skills and self-care, bowel or bladder control, play skills, or motor skills. The dramatic nature of this regression, losing the ability to speak or use the toilet after years of doing so normally, distinguished it from other forms of autism where development was delayed from the start.
How ASD Is Classified Today
The current system replaces those four labels with a single diagnosis and a severity rating. Every person diagnosed with ASD must show two core features: persistent difficulties with social communication and interaction, and restricted or repetitive patterns of behavior, interests, or activities. Within each of those two areas, the clinician assigns one of three severity levels based on how much support the person needs in daily life.
Level 1: Requiring Support
People at Level 1 can generally function independently but need some help in specific situations. Socially, they might need coaching to read facial expressions, prompting to ask for help, or guidance navigating unwritten social rules at work. Their repetitive behaviors or intense interests are present but don’t significantly interfere with daily tasks. A Level 1 profile is roughly what used to be called Asperger’s or mild PDD-NOS, though the overlap isn’t exact.
Support needs at this level often increase during transitions. Starting a new job, moving to a new city, or entering puberty can temporarily push someone’s needs higher because familiar routines and expectations have changed.
Level 2: Requiring Substantial Support
At Level 2, social communication difficulties are obvious even with support in place. A person might speak in short sentences, respond only to very direct social approaches, or have limited back-and-forth conversation. Repetitive behaviors are frequent enough to be noticeable to a casual observer and cause significant difficulty when interrupted. Flexibility with changes in routine is limited, and distress from unexpected changes can be intense.
Level 3: Requiring Very Substantial Support
Level 3 describes people with the highest support needs. Social communication is severely limited. A person may be nonverbal or use only a few words, and they rarely initiate social interaction. When they do, it may be limited to requesting basic needs. Repetitive behaviors and inflexible routines cause serious difficulty across all areas of daily life, and the person typically needs help with most everyday tasks like eating, dressing, and personal care.
Why the Levels Aren’t Fixed
One of the most important things to understand about the current system is that support levels are not permanent labels. A person can be Level 1 in social communication but Level 2 in restricted behaviors, because the two domains are rated separately. And those levels can shift over time. A child who needs very substantial support at age 4 may, after years of intervention and development, need only moderate support as a teenager. Conversely, an adult who managed well in a structured school environment may find their support needs increase when facing the less predictable demands of independent living.
This flexibility is one of the reasons the old subtypes were abandoned. Labels like “Asperger’s” or “autistic disorder” were treated as static identities, but the reality of autism is that a person’s challenges and strengths can look very different depending on their age, environment, and the support available to them.
What the Diagnosis Requires
Regardless of severity level, an ASD diagnosis requires difficulties in all three areas of social communication: social-emotional give and take (like having a back-and-forth conversation), nonverbal communication (like using and reading eye contact, gestures, and facial expressions), and building and maintaining relationships. On top of that, a person must show at least two types of restricted or repetitive behavior. These can include repetitive movements or speech patterns, insistence on sameness and rigid routines, intensely focused interests, or unusual sensitivity to sensory input like sounds, textures, light, or temperature.
Sensory differences deserve special mention because they were not part of the older diagnostic criteria. Many autistic people experience everyday sensory input differently. Some are hypersensitive, finding certain sounds painful or certain clothing textures unbearable. Others are hyposensitive, seeming barely to notice pain or temperature changes. Some are drawn to specific sensory experiences, like watching spinning objects or seeking out certain textures. The DSM-5 formally recognized these sensory features as a core part of autism for the first time.
Conditions Sometimes Confused With ASD
Rett syndrome is one condition that was historically grouped alongside autism but is now understood as a distinct genetic disorder. It results from mutations in a specific gene on the X chromosome and affects girls almost exclusively (the mutations are usually fatal in boys shortly after birth). Children with Rett syndrome may show some autism-like features, particularly repetitive hand movements like hand-wringing, but the similarities are superficial. Rett syndrome causes severe movement problems that worsen over time, including inability to walk, rigidity, and tremors. It also involves dysfunction of the autonomic nervous system that can lead to dangerous breathing abnormalities, something not seen in autism. Because the underlying cause and progression are so different, Rett syndrome is no longer classified under the autism umbrella.