Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) are both neurodevelopmental conditions that affect brain function. While distinct, they frequently co-occur and share observable features, creating a challenge for accurate diagnosis. This overlap often leads to one condition being mistaken for the other, particularly when symptoms fit the more commonly recognized profile of ADHD. Understanding the frequency of this diagnostic confusion and the subtle differences in the origin of behaviors is necessary for ensuring individuals receive appropriate support.
The Rate of Diagnostic Confusion
The question of how often autism is misdiagnosed as ADHD is complicated by the high rate at which the two conditions exist together. Since 2013, the official diagnostic manual allows for a person to be diagnosed with both. Between 30% and 80% of children diagnosed with ASD also meet the criteria for ADHD. Conversely, up to 65% of children with an ADHD diagnosis also have autistic traits.
This substantial overlap makes differential diagnosis difficult, leading to a high rate of initial misidentification. Studies suggest that 30% to 40% of children initially diagnosed with ADHD are later found to have autism. Prominent ADHD symptoms, such as hyperactivity and inattention, can effectively mask the more subtle social and communication difficulties that define ASD.
This delay is especially pronounced in girls, whose symptoms are often less outwardly disruptive than those seen in boys. Girls with a prior ADHD diagnosis experience a delay of about 2.6 years in receiving their ASD diagnosis. The tendency for some girls with ASD to “camouflage” their social difficulties means their underlying needs are often overlooked, leading to an initial, incomplete diagnosis of ADHD.
Shared Behavioral Traits
The difficulty in distinguishing the two conditions stems from several overlapping behavioral traits. Both ASD and ADHD involve challenges with executive functions, such as planning, organizing, and managing time. As a result, individuals with either condition may struggle with starting tasks, maintaining organization, and shifting attention between activities.
Difficulties with attention are a primary source of confusion, as both groups can appear distracted or unable to focus. Impulsivity is also a shared trait, manifesting as difficulty waiting for a turn. Both conditions can also present with difficulties in emotional regulation, leading to intense emotional reactions or outbursts that seem disproportionate to the situation.
Sensory sensitivities and motor restlessness further blur the lines. An autistic person may fidget or move constantly due to sensory input or anxiety, which is easily mistaken for the hyperactivity of an ADHD presentation. Similarly, social awkwardness is observed in both, as individuals may miss social cues or struggle with the back-and-forth of conversation. These surface-level behaviors can lead parents, educators, and clinicians to default to the more common ADHD diagnosis.
Distinguishing the Underlying Causes
While the outward behaviors may look similar, the underlying neurological reasons for those behaviors represent the difference between ASD and ADHD. The core issue in ADHD involves deficits in executive functions, particularly the ability to inhibit impulsive actions. An individual with ADHD struggles to filter out distractions and sustain focus on tasks they find uninteresting.
In contrast, attention difficulties in ASD are rooted in restricted interests and repetitive behaviors. An autistic person may display hyper-focus on a specific, preferred topic, appearing inattentive to everything else because their attention is intensely concentrated elsewhere. Their difficulty is not in sustaining attention, but in shifting it away from their special interest or regulating attention when overwhelmed by sensory input.
Social difficulties also stem from different causes. A person with ADHD may interrupt or miss social cues due to impulsivity and inattention to conversation details. They may want to socialize but lack the cognitive control to navigate the interaction smoothly. For an autistic person, the social challenge is rooted in a difference in social-emotional reciprocity and understanding unspoken social rules, relating directly to deficits in social communication.
The repetitive behaviors also differ in function. The restlessness of ADHD is typically a motor overflow related to poor impulse control. In ASD, repetitive behaviors, like stimming, serve a function of self-regulation and coping with stress or sensory overload. Clinicians must therefore look past the behavior itself and determine the function or motivation behind it to arrive at an accurate differential diagnosis.
Impact of Diagnostic Inaccuracy
Receiving an inaccurate or incomplete diagnosis has significant repercussions for the individual’s long-term well-being and development. The most immediate consequence is the failure of treatment to address the person’s true needs. ADHD is often managed with stimulant medication, which can be highly effective for addressing attention regulation and hyperactivity.
However, if the underlying issue is ASD, the medication will not resolve core challenges like social communication difficulties, sensory processing differences, or the need for routine. In some cases, medication intended for ADHD can even exacerbate anxiety or emotional dysregulation in an autistic person.
A missed ASD diagnosis means the individual is denied access to specialized therapeutic interventions tailored to their profile. These interventions include specialized social skills training, which helps with understanding social context and reciprocity, and occupational therapy focused on sensory integration.
When true needs are not met, individuals are more susceptible to developing co-occurring conditions, such as anxiety and depression, due to chronic stress and misunderstanding. Ultimately, diagnostic accuracy is the necessary foundation for providing support that addresses the specific neurological profile, allowing the individual to thrive.