For most of the twentieth century, the working clinical picture of autism was drawn almost entirely from observations of boys, and the working clinical picture of ADHD was drawn primarily from observations of hyperactive boys who disrupted classrooms in visible, hard-to-miss ways. These were not neutral scientific starting points; they reflected which children got referred for evaluation in the first place, which in turn reflected which behaviors adults found disruptive enough to flag. A generation of diagnostic criteria was built on this skewed referral pattern, and the consequences of that foundational bias are still being untangled by researchers and clinicians today.
The Scale of the Diagnostic Gap
The resulting sex disparities in diagnosis rates are substantial. Autism has historically been diagnosed in boys at roughly three to four times the rate of girls, and while that ratio has narrowed as diagnostic understanding has improved, it has not closed, and most researchers in the field now believe the true underlying prevalence gap between sexes is considerably smaller than the diagnosed gap, meaning a significant number of autistic girls and women are simply not being identified. ADHD shows a similar pattern, with boys historically diagnosed at two to three times the rate of girls, again a gap that researchers increasingly attribute to differences in presentation and referral rather than to a true difference in underlying prevalence of that magnitude.
How Masking Hides Autism in Girls
Several factors appear to converge to produce this gap. Girls with autism appear, on average, to engage in more extensive social masking than boys, developing compensatory strategies such as scripted conversation, careful observation and imitation of peer behavior, and suppression of stimming, that allow them to superficially blend into typical peer social groups even while experiencing the same underlying social confusion and sensory distress as a more visibly autistic male peer. A teacher or clinician looking for the stereotypical presentation, marked social withdrawal, limited eye contact, overt stimming, may simply not see it in a girl who has learned to camouflage those traits, even though the internal experience and the eventual mental health cost of that camouflaging are substantial.
Special interests present a related pattern worth noting specifically. Diagnostic criteria for autism reference intense, narrowly focused interests as a core feature, and clinicians trained on male-typical presentations have historically looked for stereotypically unusual interest topics, such as train schedules or technical specifications, as a diagnostic signal. Autistic girls often develop equally intense and narrowly focused interests, but frequently in topics that are more socially conventional for girls, animals, particular fictional franchises, or celebrities, which makes the same underlying trait, an intensely focused, unusually deep and exclusive interest, far less likely to register as a diagnostic red flag to an observer looking for a more stereotypically atypical topic.
ADHD's Subtype Bias
ADHD presents its own sex-linked diagnostic bias, centered less on masking and more on subtype. The hyperactive-impulsive presentation of ADHD, the stereotype of a boy who cannot sit still and interrupts constantly, is more disruptive to classroom management and therefore more likely to trigger a teacher referral. The inattentive presentation, characterized by daydreaming, difficulty sustaining focus on tedious tasks, and disorganization without accompanying hyperactivity, is both more common in girls on average and far less likely to prompt a referral, since a quietly inattentive student causes no classroom disruption and may simply be labeled unmotivated, a poor student, or a daydreamer rather than flagged for evaluation.
The Cost of Being Misdiagnosed
The downstream consequences of this diagnostic gap extend well beyond the delayed label itself. Women diagnosed with autism or ADHD in adulthood frequently report years of misdiagnosis with anxiety, depression, borderline personality disorder, or bipolar disorder, conditions that share surface-level symptom overlap but require substantially different treatment approaches, and the mismatch between treatment and underlying condition can leave the actual driver of distress unaddressed for years or decades. There is also a compounding effect: without an accurate diagnostic framework to make sense of their experience, many women describe attributing chronic difficulties to personal failing rather than to an unrecognized neurodevelopmental difference, with real consequences for self-esteem and mental health that accumulate over an extended period of undiagnosed struggle.
Clinical training is gradually incorporating this research, and diagnostic tools are being revised to better capture female-typical presentations, including updated interview protocols that specifically probe for masking behavior and camouflaged special interests rather than relying solely on observable, stereotypically male-typical markers. But revision of entrenched diagnostic assumptions moves slowly, and most clinicians practicing today were trained on the older, narrower model. Closing the remaining gap will likely require sustained effort on multiple fronts simultaneously, continued refinement of diagnostic criteria, broader clinician training on the full range of presentations, and a cultural shift away from the assumption that neurodivergence has a single default appearance, an assumption that has left a great many capable, struggling women waiting far longer than they should have for a framework that could have helped explain their own lives to them.
