Autistic Adults in England May Be Double the Estimate
Author: University College London
Published: 26 Jun 2023 - Updated: 15 Jul 2026
Publication Details: Peer-Reviewed | Research, Study, Analysis
Table of Contents:
Synopsis - Definition - Overview - FAQs - Insights, Updates - Related Content
Synopsis
This research is a peer-reviewed, population-based study by University College London, published in The Lancet Regional Health Europe, that estimates how many adults in England are autistic but have never been diagnosed. Drawing on anonymized records from more than 5 million people registered at GP practices between 2000 and 2018, the team compared recorded diagnoses against lower and upper estimates of true autism prevalence and concluded that roughly 750,000 adults aged 20 and over may be undiagnosed, pushing the real autistic population past 1.2 million. The work carries weight because it uses primary care data on a large scale rather than smaller surveys, and it speaks directly to autistic adults, seniors, and their families by making the case that a formal diagnosis opens the door to reasonable adjustments and support in health care, employment, and daily life that many people are currently missing.*
At a Glance
- 1 - As of 2018, only about 180,000 people aged 20 and over had an autism diagnosis, meaning most autistic adults in England were unrecognized.
- 2 - Among autistic people over the age of 50, more than 9 in 10 may be undiagnosed, with an estimated 250,000 to 600,000 in that age group alone.
- 3 - The upper prevalence estimate was drawn from diagnosis rates in young people aged 10 to 19, since autism is now more readily recognized in that age group than in older adults.
Topic Definition
- Undiagnosed Autism in Adults
Undiagnosed autism in adults refers to people who meet the criteria for autism spectrum condition but have never received a formal clinical diagnosis, often because autism was long treated as something identified only in childhood. Autistic people may show differences in social communication and social interaction, along with restricted or repetitive patterns of behavior, interests, and activities, yet these traits can go unrecognized in adults who have learned to mask them or who grew up before diagnostic criteria became more inclusive. The practical significance is considerable, because without a diagnosis a person cannot easily advocate for reasonable adjustments or access tailored support in health care, employment, and local services, which is why researchers increasingly frame adult under-diagnosis as a gap in recognition rather than a true absence of the condition.
Overview
"Autism in England: Assessing Under diagnosis in a Population-Based Cohort Study of Prospectively Collected Primary Care Data" - The Lancet Regional Health Europe.
The true number of autistic people in England may be more than double the number often cited in national health policy documents, suggests a new study by UCL researchers.
The first-of-its-kind research, published in The Lancet Regional Health Europe, estimated how many adults in England may have undiagnosed autism.
To do this, the researchers calculated the number of people who had received an autism diagnosis, from anonymised data from more than 5 million individuals registered at GP practices in England between 2000 and 2018.
They then compared these figures with a lower (c.1%) and upper (c.3%) estimate of how common autism really is in the population.
The lower estimate was based on the widely stated figure that around 1% of people in England are autistic. This came from epidemiological research published in 2011, before changes to the diagnostic criteria for autism that made them more inclusive.
Meanwhile, the upper estimate was based on rates of diagnosed autism in young people (aged 10-19) in the researchers' dataset. This is because young people are most likely to have had their autism recognised since providers are now very aware of autism in young people.
The team's estimates suggest that between 150,000 and 500,000 people aged 20 to 49 years-old may be autistic but undiagnosed.
Meanwhile, between 250,000 and 600,000 autistic people over the age of 50 may be undiagnosed - more than 9 in 10 of all autistic people.
The midpoint of these figures translates to approximately 750,000 undiagnosed autistic people aged 20 and above, in England. This brings the total autistic population to over 1.2million - approaching double the figure of 700,000 cited by the government for the entirety of the UK*.
Now researchers are calling for better access to diagnostic services for adults, and better support after diagnosis.
They also want to encourage greater acceptance and understanding of neurodiversity in society.
Lead researcher, post-doctoral researcher Elizabeth O'Nions (UCL Psychology & Language Sciences), said:
"Historically, autism has been considered as a condition of childhood. But recently, awareness has been growing that it is present across the lifespan - in adults as well as young people."
"Nevertheless, autism is still under-recognised in adults. Our estimates suggest that about 180,000 people aged 20-plus had an autism diagnosis as of 2018, meaning that most autistic adults in England were undiagnosed."
"This matters because autistic people often experience discrimination and exploitation in society. They may have unmet support needs, even when they appear to be coping with life."
"Having a diagnosis means that someone can advocate for their right to reasonable adjustments and the support they need. Recognising that someone with an intellectual disability is autistic can also help people to understand and support them better."
Autistic people may exhibit signs such as differences in their social communication and social interaction, alongside restricted and repetitive patterns of behaviours, interests and activities.
Many autistic people require adjustments to be made to ensure equal access healthcare, employment, and local authority support.
Dr O'Nions added:
"Our findings indicate that there is still a substantial diagnostic gap in adults compared to children and young people when it comes to autism in England."
"This may partly reflect a lack of awareness and understanding of autism in adults on the part of healthcare professionals. Older adults may also be less likely to self-identify as autistic, meaning that they do not come to the attention of services."
"Meanwhile, providers may be hesitant to raise the issue of autism given the uncertainty around waiting times for a diagnosis and the availability of support or specialist services post-diagnosis."
The research was funded by Dunhill Medical trust, Economic and Social Research Council, Medical Research Council, National Institute for Health and Care Research, Wellcome, and the Royal College of Psychiatrists.
Study Limitations
Primary care records are not directly linked to secondary care records, which could mean that some diagnoses are not represented in the study.
Meanwhile, the data does not cover all English GP practices, meaning that it wasn't possible to map local variation in diagnostic rates at a granular level.
Frequently Asked Questions
NOTE: Researched FAQs by Disabled World (DW)
Why are so many autistic adults undiagnosed?
For decades autism was viewed mainly as a childhood condition, so many adults grew up before awareness and diagnostic criteria expanded. Older adults may also mask their traits or not think of themselves as autistic, meaning they never come to the attention of services.
What are the benefits of getting an autism diagnosis as an adult?
A formal diagnosis allows a person to request reasonable adjustments and support in health care, work, and daily life to which they may be entitled. It can also help family, employers, and professionals better understand and accommodate an individual's needs.
How did the diagnostic criteria for autism change?
Diagnostic criteria were revised over time to become more inclusive, recognizing a broader range of presentations across the spectrum. Because earlier prevalence estimates predated these changes, they tended to undercount how common autism actually is.
What is the difference between autism prevalence and diagnosis rates?
Prevalence is an estimate of how many people in a population actually have a condition, while the diagnosis rate reflects only those formally identified by services. A wide gap between the two, as seen with adult autism, points to substantial under-diagnosis rather than a low true prevalence.
What support is available for autistic adults after diagnosis?
Support can include workplace and healthcare adjustments, local authority assistance, and access to specialist services, though availability varies and waiting times can be long. The study's authors specifically called for improved access to both diagnostic services and post-diagnosis support for adults.
Why is primary care data useful for studying autism prevalence?
Primary care records cover very large numbers of people over many years, allowing researchers to estimate diagnosis patterns across age groups at a scale that smaller surveys cannot match. The trade-off is that such records may miss diagnoses made in secondary care and do not always capture local variation.
Insights, Analysis, and Developments
Editorial Note: The gap this study describes is less about how common autism is and more about who gets seen, since the researchers found that recognition drops off sharply with age while the condition itself does not. Part of the explanation, the authors suggest, is circular: older adults are less likely to identify as autistic and come forward, while clinicians may hesitate to raise the subject when waiting times are long and post-diagnosis support is thin, so the very scarcity of services helps keep the numbers low. The team is careful about its limits, noting that primary care records are not linked to secondary care and do not cover every practice, yet the central message holds, namely that treating autism as a childhood condition has left a large, mostly older population without the diagnosis that would let them ask for the adjustments they are entitled to.*
Attribution/Source(s): This peer reviewed publication was selected for publishing by the editors of Disabled World (DW) due to its relevance to the disability community. Originally authored by University College London and published on 26 Jun 2023, this content may have been edited for style, clarity, or brevity.
* Editorial additions by Ian C. Langtree.