ADHD and autism: why they overlap so often, and how OT and physio can help

By Helen & Sam, Three Therapy

If your child has an ADHD diagnosis and you've also started wondering about autism (or the other way around), you're noticing something real. These two conditions co-occur far more often than most people expect, and understanding why can make a real difference to how you support your child.

Just how much do they overlap?

The honest answer is: a lot, though the exact numbers vary a lot between studies. Depending on how researchers measure it, somewhere between one in five and more than half of children with ADHD also show clinically significant autism traits — and a similarly wide range of children on the autism spectrum meet the criteria for ADHD. Twin and family studies suggest a substantial share of the genetic factors behind the two conditions overlap, which is likely a big part of why they show up together so often. You may have come across the informal term "AuDHD" — it's not a formal clinical diagnosis, but it's widely used within the neurodivergent community to describe this specific combination.

Why the overlap happens

Autism and ADHD are diagnosed based on different criteria — autism centres on social communication and restricted or repetitive patterns, ADHD centres on attention and impulse regulation — but underneath, they draw on a lot of the same brain systems: executive function, attention regulation, and sensory processing. That shared foundation is likely why a lot of traits genuinely blur between the two, and why one condition can sometimes mask or be mistaken for the other, especially in kids who haven't been formally assessed for either.

What it can actually look like

Every child is different, but some patterns come up often when both are present:

• Intense, hyperfocused interest in specific topics, alongside real difficulty shifting attention when asked
• Sensory seeking and sensory avoiding behaviours showing up in the same child, depending on the type of input
• Motor coordination difficulties — clumsiness, trouble with handwriting, or avoiding sport — turning up alongside attention differences
• Big meltdowns that seem to come from a combination of sensory overwhelm and difficulty regulating impulses at the same time
• Social difficulties that don't fit neatly into either an "autism-only" or "ADHD-only" pattern

Why getting the fuller picture matters

Because these conditions can mask each other, a child assessed for only one may end up with a plan that doesn't quite fit — strategies designed purely for ADHD can miss the sensory and social pieces, and strategies designed purely for autism can miss the attention and impulse regulation piece. Working with clinicians who look at the whole picture, rather than ticking boxes for a single diagnosis, tends to lead to support that actually reflects how your child experiences the world.

As with the rest of what we've written about, you don't need to arrive with a clear diagnosis or a clean label before reaching out. Tell us what you're actually noticing, and we'll help you work out what kind of support fits.