The short answer
Autism and ADHD are different conditions, but they overlap more than most people expect. Both can affect attention, friendships, emotions and how someone copes with everyday demands. Studies suggest that roughly three to four in ten autistic people also have ADHD. That is why a combined assessment, where one team looks at both at the same time, usually gives the clearest and most useful answer.
What autism looks like
The NHS describes autism as differences in how someone communicates, behaves and reacts to the world. In children, signs can include using eye contact less often, very strong interests, getting worried or upset by changes in routine, and reacting very strongly, or not at all, to lights, sounds, smells, tastes or textures. Adults may take things literally, have fixed ways of doing things and become distressed when routines change.
What ADHD looks like
ADHD is mainly about attention, activity and impulse control. The NHS says symptoms in children and teenagers usually start before the age of 12 and fall into three groups: being inattentive, hyperactive and impulsive. Adults often describe finding it hard to organise their time, losing things often and making quick decisions without thinking about what might happen.
Why they are so easy to confuse
From the outside, the two can look almost the same. A child who does not listen in class may be distracted by their own thoughts (more typical of ADHD), or overwhelmed by noise and focused on something that matters more to them (more typical of autism). An adult who struggles at work may find it hard to start tasks, or may find open-plan offices and unwritten social rules exhausting. The behaviour is similar; the reason behind it is not.
Getting that reason right matters, because it changes the advice and support that actually help. That is the job of a proper assessment, not a questionnaire.
At a glance
- Roughly 3 to 4 in 10 autistic people also have ADHD, depending on the study.
- Until 2013, the main diagnostic manual (DSM) did not allow both diagnoses at once. DSM-5 changed that.
- Girls and women are more often missed, because they tend to mask or have quieter, inattentive symptoms.
- NICE guidance allows children with signs of both to be assessed for both together.
Sources: Lai et al., Lancet Psychiatry 2019 (28%), Rong et al., 2021 (38.5%), American Psychiatric Association, NICE CG128. Checked 30 September 2026.
How common is it to have both?
Very common. A large review in The Lancet Psychiatry (2019) found that around 28% of autistic people also have ADHD, and a meta-analysis of 63 studies (2021) put the figure at 38.5%. The National Autistic Society notes that it is quite common for autistic people to also receive an ADHD diagnosis, sometimes called «AuDHD».
Before 2013, the diagnostic manual used by clinicians did not allow ADHD to be diagnosed alongside autism. DSM-5 changed that, which is one reason so many people only now discover they have both.
Girls, women and masking
The NHS says it can be harder to see the signs of autism in girls because of masking: copying how other children behave and appearing to cope, often at a real cost in anxiety and exhaustion. ADHD is also recognised less often in women, partly because inattentive symptoms are quieter than hyperactivity. The National Autistic Society says many autistic women and girls struggle to get a diagnosis, are diagnosed late or are misdiagnosed. An experienced clinician knows to look beneath the surface.
Why a combined assessment makes sense
NICE guidance for children (CG128) says children with ADHD are more likely to be autistic, and allows joint assessment for both conditions when the signs could be caused by either. Guidance for adults (CG142) and for ADHD (NG87) asks clinicians to look for coexisting neurodevelopmental conditions as part of the assessment.
In practice, being assessed for one condition and then waiting again for the other can take years. With us, autism and ADHD can be assessed together in one combined assessment, by licensed clinical psychologists, at one price. You get one clear written report that explains the whole picture. See what it costs and what happens on the day.
When is it worth getting assessed?
- The signs have been there for a long time, not just during a hard few weeks.
- They affect school, work, friendships or family life.
- You or your child have been told «it’s just behaviour», «just anxiety» or «they’ll grow out of it», and it does not fit.
- You are an adult who has wondered for years, often after a child in the family was assessed.
If that sounds familiar, you do not have to spend years on a waiting list to get an answer. We arrange assessments for children and adults, and the first call is free.
Frequently asked questions
Can you have autism and ADHD at the same time?
Yes. Since DSM-5 in 2013, both can be diagnosed together, and studies suggest roughly 3 to 4 in 10 autistic people also have ADHD.
What is the main difference between autism and ADHD?
Autism is mainly about differences in communication, social interaction, routines and sensory experience. ADHD is mainly about attention, hyperactivity and impulsivity. The same behaviour can have different causes, which is why an assessment looks at both.
Why are girls and women diagnosed later?
Girls and women more often mask their difficulties or have quieter, inattentive symptoms, so the signs are easier to miss.
Can I be assessed for both at the same time?
Yes. We offer a combined autism and ADHD assessment for children and adults, with one written report.
