Autism is not the same thing as intellectual disability (formerly called “mental retardation”). They are two separate diagnoses with different defining features, different causes, and different effects on daily life. While they can occur together in the same person, the majority of autistic individuals do not have an intellectual disability at all.
Two Distinct Conditions
Autism spectrum disorder is defined by differences in social communication and by restricted or repetitive patterns of behavior and interests. An autistic person may struggle to read social cues, maintain back-and-forth conversation, or adapt to changes in routine. These traits exist across a wide range of intellectual ability, from people with very high IQs to those with significant cognitive delays.
Intellectual disability, by contrast, is defined by limitations in general cognitive functioning (typically an IQ below 70) combined with difficulty managing everyday tasks like handling money, following schedules, or caring for oneself. The key distinction: intellectual disability affects broad thinking and learning ability, while autism specifically affects social communication and behavioral flexibility. A person can have one, both, or neither.
Both the American Psychiatric Association’s diagnostic manual and the World Health Organization’s international classification system treat autism and intellectual disability as separate diagnoses. When both are present, clinicians are expected to assign each one individually rather than folding one into the other.
How Often They Overlap
CDC surveillance data from 2020 found that among children with autism who had cognitive testing on record, 37.9% were classified as having an intellectual disability. Another 23.5% fell in a borderline range (IQ 71 to 85), and 38.6% scored in the average or higher range. In other words, nearly two out of three autistic children with available test data did not meet the threshold for intellectual disability.
These numbers have shifted dramatically over the past few decades. Earlier studies from the 1990s and before often reported much higher rates of co-occurring intellectual disability in autism, sometimes above 70%. The change reflects broader diagnostic criteria that now capture autistic people across the full IQ spectrum, not just those with the most visible support needs.
Why the Two Were Confused for Decades
For much of the 20th century, many autistic people were simply labeled “mentally retarded” and placed in institutions. Autism wasn’t widely recognized as its own condition, and the behaviors associated with it, such as limited speech, difficulty following instructions, and social withdrawal, were interpreted as signs of low intelligence. Children who didn’t speak or couldn’t perform on standardized tests were assumed to have a global cognitive deficit, even when their actual intellectual capacity was much higher than test results suggested.
Starting in the 1960s, large institutions for people labeled “mentally defective” began closing in the United States and Britain. As former residents moved into community settings and schools, clinicians developed better tools for distinguishing between different developmental conditions. Speech therapy services expanded, and researchers began to recognize that a child’s inability to communicate didn’t necessarily reflect an inability to think. By the 1980s, diagnostic methods had improved enough to identify autism as a distinct pattern, separate from intellectual disability, though the two could still co-occur.
Why the Term Changed
The phrase “mental retardation” is no longer used in U.S. law or in major diagnostic systems. In 2010, Congress passed Rosa’s Law, which replaced the term in federal statutes with “intellectual disability.” The American Psychiatric Association followed suit in 2013, dropping “mental retardation” from its diagnostic manual entirely. The reasoning was straightforward: the older term had become derogatory, carried heavy stigma, and led to misunderstandings about what the condition actually involves. The condition itself didn’t change. The diagnostic criteria remained the same. Only the label was updated.
IQ Doesn’t Tell the Whole Story in Autism
One of the most important things to understand about autism is that IQ scores can be misleading in both directions. An autistic person with an average or high IQ may still struggle significantly with daily life skills, particularly in social situations. Research consistently shows that adaptive behavior, meaning the practical ability to navigate everyday tasks and social interactions, is often much more impaired in autistic people than their IQ would predict. This gap is especially pronounced in social functioning: IQ does a poor job of predicting how well an autistic person handles relationships, reads social situations, or lives independently.
This disconnect works the other way too. Some autistic individuals score poorly on standard IQ tests because those tests rely heavily on verbal communication, timed responses, or the ability to interact with an examiner. A person who can’t easily produce speech on demand may appear to have an intellectual disability on a standardized test while possessing strong cognitive abilities that the test simply wasn’t designed to capture.
This is why autism uses its own severity framework based on support needs rather than IQ. The three levels, ranging from “requiring support” to “requiring very substantial support,” describe how much help a person needs with communication and daily functioning. Someone at Level 1 may live independently with minimal accommodations. Someone at Level 3 may need round-the-clock assistance. Neither level is determined by intelligence alone.
What This Means in Practice
If you or someone you know has autism, it’s worth understanding that an intellectual disability diagnosis requires its own separate evaluation. The two conditions call for different types of support. Autism-specific interventions focus on social communication skills, sensory needs, and behavioral flexibility. Intellectual disability support focuses on building cognitive and practical life skills across all areas of functioning.
When both conditions are present, the diagnostic process becomes more nuanced. Clinicians need to determine whether social difficulties are caused by autism specifically or are simply consistent with what you’d expect at a given cognitive level. Both the DSM-5 and the ICD-11 emphasize that when evaluating for intellectual disability in an autistic person, the assessment should focus more heavily on practical and conceptual skills rather than social skills, since social difficulties are already a core feature of autism itself.
The bottom line: autism and intellectual disability are separate conditions that happen to overlap in roughly a third of cases. Having one does not mean having the other, and assuming they’re the same thing can lead to support that misses what a person actually needs.