ADHD vs autism: how to tell the difference (and why it’s often both)

This guide walks through what genuinely differs, where they overlap, why “both” is a real answer, and how assessment works in Singapore.

In our home, we honestly can’t tell

Our daughter is autistic — and she also can’t sit still for more than ten minutes, fidgets constantly, sings and talks to herself, struggles to wait for her turn or for something she wants, and tunes us out completely when she’s absorbed in something she loves. Are those autism? ADHD? Both?

We’ve read the checklists, and she half-matches all of them. If you’ve been going in circles trying to sort your child’s behaviour into one column or the other, we can’t hand you a trick that settles it — because after years of living with it, we can’t always sort it either.

What we can tell you is why it’s so hard, what genuinely differs between the two, and why “both” is a real and common answer.

What is ADHD? What is autism?

Plain language first, labels second. Both are neurodevelopmental — differences in how a brain develops and works, present from early childhood, lifelong. Neither is an illness to cure, and neither is caused by parenting.

Autism (autism spectrum disorder, ASD) is a difference in how a person experiences and connects with the world. The core threads: social communication works differently (reading cues, back-and-forth interaction), there’s comfort in repetition and routine, interests can run deep and intense, and the senses are often tuned differently — sounds, textures, lights can be much more (or less) intense.

ADHD (attention deficit hyperactivity disorder) is a difference in how a brain regulates attention, impulses, and activity. In children it shows up as some mix of inattentiveness — easily distracted, hard to listen or follow instructions, everyday tasks forgotten — and hyperactivity-impulsivity — fidgeting, restlessness, getting up when they’re supposed to sit, finding it hard to wait their turn, interrupting. Most children with ADHD show a combination of both; some show mainly one. Worth knowing for parents of girls: girls more often show the quieter, inattentive side, which is easier to miss.

Notice something? Half the ADHD list could describe plenty of autistic children too. That’s not sloppy writing — it’s the actual problem, and it’s next.

The real differences, side by side

These are the tendencies clinicians look at. Read the table, then read the caveat under it — the caveat matters more.

Why they’re so easy to confuse

Because from the outside, the overlap is bigger than the difference. Peer-reviewed reviews put it plainly: both conditions often involve difficulty with attention, communication with peers, impulsivity, and restlessness. The behaviours look the same at the playground; what differs is the machinery underneath.

Take “not listening.” An autistic child may not orient to voices because social attention runs on a different track. A child with ADHD hears you, but their attention has already been pulled three things away. Same silence, different reasons — and the support that helps is different, which is why the distinction is worth pursuing properly rather than settling by gut feel.

And sometimes there’s no clean underneath to find, because it’s genuinely both.

Can a child have both? Yes — and it’s common

This is the part the “versus” framing hides. Autism and ADHD frequently occur together. Studies commonly report that roughly a third to a half of autistic children also show ADHD symptoms, and features of autism are common in children with ADHD too. The overlap is so common that the diagnostic rulebook changed for it: until 2013, the manual said an autism diagnosis excluded ADHD — the DSM-5 removed that rule specifically because the co-occurrence was too frequent to ignore.

You may also see the informal word “AuDHD” in parent communities — not a diagnosis, just shorthand for having both.

This is where we stop being neutral narrators: our daughter may well be an example. She’s autistic, and the fidgeting, the ten-minute ceiling on sitting still, the trouble waiting — those read like the ADHD column. We haven’t settled it, and honestly, the label matters less to us than the support does. Which is the practical point: if both are present, support should address both — strategies for one can miss the other entirely.

Getting it assessed in Singapore

The good news: you don’t have to solve “which one” before seeking help, because in Singapore both go through the same front door. Developmental and behavioural concerns — social communication, attention, activity level, all of it — are assessed via a GP or polyclinic referral to KKH’s Department of Child Development or NUH’s Child Development Unit, or through a private developmental paediatrician.

• Describe everything you see, not just one column. A thorough assessment looks at the whole picture, and it can only weigh what you report. The fidgeting and the lining-up of toys. The interrupting and the distress at changed plans.
• Don’t pre-filter. If you’ve privately decided “it’s probably ADHD,” you might underreport the social-communication patterns — and vice versa. Bring the confusion itself; it’s useful clinical information.

If you’re starting from scratch, our step-by-step guide to getting an autism diagnosis in Singapore covers the route, the waits, and the costs — the process is the same road regardless of which condition (or combination) the assessment finds.