Hidden in Plain Sight: Why Autism Gets Overlooked in ADHD Tests
Updated: Sep 6
Autism is often missed during ADHD assessments because the two conditions share symptoms like inattention and social difficulties, older diagnostic rules once banned a dual diagnosis, and many autistic people—especially girls—mask their traits. As a result, autism can go unrecognized for years after an ADHD diagnosis.
Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) show up together far more often than most people realize. Research estimates that 50% to 70% of autistic individuals also meet the criteria for ADHD (Leitner, 2014). Yet despite this strong overlap, autism is regularly missed when someone is being assessed specifically for ADHD.
Why does this happen? The reasons are part clinical, part historical, and part human. When a child fidgets, interrupts, and struggles to focus, ADHD becomes the obvious explanation—and once that label sticks, the quieter signs of autism can fade into the background.
This post breaks down the main reasons autism slips under the radar during ADHD evaluations. Each section draws on peer-reviewed research, but the goal is plain language, not jargon. Whether you're a parent, an educator, or someone questioning your own diagnosis, you'll walk away understanding why so many autistic people wait years for the full picture to come into focus.
Why do autism and ADHD get confused so easily?
The short answer: they share a lot of the same surface features. Both conditions involve challenges with executive functioning (the brain's ability to plan, organize, and manage tasks), emotional regulation, and social interaction (Rommelse et al., 2010).
Because the two overlap so much, clinicians can fall into a trap called diagnostic overshadowing. This is when one prominent diagnosis—ADHD, in this case—soaks up all the attention, and the clinician attributes everything the patient experiences to that single condition. The unique features of autism get folded into the ADHD explanation and disappear.
Here's how that plays out in practice:
Social difficulties get misread. In ADHD, trouble with friendships is often chalked up to impulsivity or inattention—interrupting people, losing the thread of a conversation, forgetting to reply. A clinician may not stop to consider that these same struggles can stem from autism's core differences in social-emotional reciprocity and reading nonverbal cues.
Routines get mislabeled. Both groups struggle with transitions and organization. But when an autistic person becomes distressed because their routine changed, that reaction can be misread as ADHD-related emotional swings or impulsivity, rather than an autistic need for sameness and predictability.
Rommelse and colleagues (2010) point out that ADHD and autism even share some of the same genetic and neuropsychological roots. So the confusion isn't sloppy work—it reflects genuine biological overlap between the two conditions.
How did old diagnostic rules make this worse?
For a long time, the rulebook itself made a dual diagnosis impossible.
Before the DSM-5 was published in 2013, the official criteria flat-out prohibited diagnosing someone with both autism and ADHD. Under the earlier DSM-IV, a diagnosis of a Pervasive Developmental Disorder (which included Autistic Disorder and Asperger's Disorder) automatically ruled out ADHD—and the reverse was true, too.
That single rule shaped how an entire generation of clinicians was trained. Assessment methods became siloed: you evaluated for one condition or the other, not both together. Leitner (2014) reviewed the clinical fallout from this and explained how ADHD symptoms often mask underlying autism, which pushes an ASD diagnosis further and further down the road.
The DSM-5 removed the mutual-exclusivity rule, so a dual diagnosis is now perfectly valid. The problem is that habits and tools haven't fully caught up. Many standardized assessments and clinical pathways are still built around a single condition, and they don't automatically prompt clinicians to screen for both (Leitner, 2014).
Why is autism missed more often in girls and high-masking adults?
One of the biggest reasons autism goes unnoticed is a behavior called camouflaging or masking.
Masking is the effort autistic people put into copying neurotypical behavior—rehearsing conversations, forcing eye contact, mimicking facial expressions, and hiding the things that feel natural to them. It's especially common among autistic individuals with average to high cognitive ability, and among girls and women (Kopp et al., 2010).
Now think about what an ADHD assessment usually looks like: a structured session in an unfamiliar clinic, often relying on self-report questionnaires and short bursts of observed behavior. That setting is almost tailor-made to let masking succeed. A skilled masker can hold their social differences together just long enough for the appointment to end, so the clinician never sees them.
Meanwhile, the classic signs of ADHD—restlessness, blurting things out, physical fidgeting—are loud and visible. Teachers, parents, and clinicians notice them immediately. Autism's traits, by contrast, are often internal and hidden. Kopp and colleagues (2010) found that girls who came in with ADHD symptoms frequently had unrecognized autistic traits, overlooked precisely because their social masking was so effective.
The result is predictable: the assessment zeroes in on the noisy, externalizing ADHD behaviors and misses the quiet, internalizing autistic ones.
Do standard ADHD tests actually screen for autism?
Not really—and this is a technical limitation worth understanding.
Popular ADHD rating scales, such as the Conners Rating Scales and the ADHD Rating Scale-5, are very good at detecting ADHD symptoms. In clinical terms, they have high sensitivity. What they lack is specificity: they don't tell you why a behavior is happening.
Consider a single item like "difficulty playing quietly." A parent might answer "yes" for an ADHD child because that child is hyperactive and can't sit still. But a parent might also answer "yes" for an autistic child—not because of hyperactivity, but because the child prefers solitary play or is deeply absorbed in a special interest. Same checkbox, completely different reason.
Without a thorough developmental history that specifically asks about autistic traits, these distinctions vanish. Gargaro and colleagues (2011) compared the cognitive and behavioral profiles of the two conditions and showed how easily autism's distinct social-communication differences get missed when a clinician's attention is fixed on attention and hyperactivity alone.
How much does an ADHD diagnosis delay an autism diagnosis?
This is where the consequences become concrete—and measurable.
Miodovnik and colleagues (2015) studied the timing of both diagnoses and found something striking: children who were first diagnosed with ADHD received their autism diagnosis an average of three years later than children who did not have an initial ADHD diagnosis.
Three years is a long time in a child's development. It can mean missed early intervention, the wrong supports at school, and mounting frustration for families who sense something more is going on but can't get answers. The study offers hard evidence that an early ADHD label doesn't just sit alongside autism—it can actively delay its recognition.
What this means for families, educators, and clinicians
If autism and ADHD overlap this much, the practical takeaway is simple: an ADHD diagnosis should be treated as a starting point, not the final word.
Here's how that plays out depending on who you are:
Choose a comprehensive evaluation if masking is a concern. If the person being assessed is a girl, a woman, or a verbally capable adult who "seems fine" socially in short interactions, a standard ADHD screening may not be enough. A full developmental history that probes for autistic traits gives a far more accurate picture.
Push for both conditions to be considered if symptoms don't fully add up. When an ADHD diagnosis explains some struggles but leaves others—like intense need for routine, sensory sensitivities, or deep special interests—unaccounted for, it's worth asking a clinician directly about autism.
Look beyond the disruptive behaviors if you're a clinician or educator. The loudest symptoms aren't always the most important ones. Distress during transitions, rigid routines, and social differences deserve their own investigation rather than being filed under ADHD by default.
None of this means ADHD diagnoses are wrong. Often they're accurate—just incomplete. The goal is to see the whole person, not just the parts that make the most noise.
Frequently asked questions
Can you have both autism and ADHD at the same time?Yes. Since the DSM-5 was published in 2013, clinicians are allowed to diagnose both conditions together. Research suggests 50% to 70% of autistic individuals also meet the criteria for ADHD (Leitner, 2014), so co-occurrence is common rather than rare.
Why is autism missed more often in girls than boys?Autistic girls tend to be more effective at social camouflaging—copying neurotypical behavior to blend in. Kopp and colleagues (2010) found that girls presenting with ADHD symptoms often had unrecognized autistic traits that were overlooked because their masking hid the social differences a clinician would otherwise notice.
What is diagnostic overshadowing?Diagnostic overshadowing happens when one prominent diagnosis absorbs all the clinical attention, so other conditions get missed. With ADHD, its visible symptoms—hyperactivity, impulsivity, inattention—can lead a clinician to attribute everything to ADHD, overlooking autism's quieter, overlapping features (Rommelse et al., 2010).
Do ADHD tests screen for autism?Generally, no. Standard tools like the Conners Rating Scales and the ADHD Rating Scale-5 are sensitive to ADHD symptoms but don't identify why a behavior occurs. Without a developmental history that asks specifically about autistic traits, autism can easily be missed (Gargaro et al., 2011).
How long can an autism diagnosis be delayed after an ADHD diagnosis?On average, about three years. Miodovnik and colleagues (2015) found that children diagnosed with ADHD first received their autism diagnosis roughly three years later than children without an initial ADHD diagnosis.
Should I get reassessed if I was only diagnosed with ADHD?If your ADHD diagnosis doesn't fully explain your experiences—especially around routines, sensory sensitivity, social exhaustion, or masking—it may be worth asking a clinician about a comprehensive autism assessment. This is particularly relevant for women and verbally capable adults whose autistic traits are easy to overlook.
References
Gargaro, B. A., Rinehart, N. J., Reichenberg, A., Sheppard, D. M., & Tonge, B. J. (2011). Autism and ADHD: How do they differ? Journal of Attention Disorders, 15(3), 203–211.
Kopp, S., Beckung, E., & Gillberg, C. (2010). Developmental profiles and cognitive abilities in girls with ADHD, autism spectrum disorders, and adjacent disorders. Journal of Attention Disorders, 14(3), 203–215.
Leitner, Y. (2014). The co-occurrence of autism spectrum disorder and attention deficit hyperactivity disorder in children. Scientific World Journal, 2014, 861219.
Miodovnik, A., Harstad, E., Sideridis, G., & Huntington, N. (2015). Timing of the diagnosis of attention-deficit/hyperactivity disorder and autism spectrum disorder. Pediatrics, 136(4), e830–e837.
Rommelse, N. N., Franke, B., Geurts, H. M., Hartman, C. A., & Buitelaar, J. K. (2010). Shared heritability of attention-deficit/hyperactivity disorder and autism spectrum disorder. European Child & Adolescent Psychiatry, 19(3), 281–295.
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