A large Swedish study tracking 2.7 million people born between 1985 and 2020 has found something that challenges decades of assumptions: autism rates between boys and girls are nearly identical by age 20. The catch is in how we get there.
Boys are diagnosed roughly three to four times more often than girls before age 10. The median diagnosis age for boys sits at 13.1 years; for girls, it's 15.9. That's almost a three-year gap that compounds into missed support, misunderstood struggles, and years spent thinking something is wrong with you rather than understanding how your brain works differently.
By early adulthood, though, the numbers converge. Girls catch up during adolescence in a rapid surge of diagnoses — which tells researchers something important: the difference was never about who is actually autistic. It was about who got noticed.
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Start Your News DetoxWhy Girls Disappear from the Statistics
Dr Caroline Fyfe, who led the research at Sweden's Karolinska Institutet, puts it plainly: "Our findings suggest that the gender difference in autism prevalence is much lower than previously thought, due to women and girls being underdiagnosed or diagnosed late."
The reasons are tangled. Girls are more likely to mask their autistic traits — suppressing stimming, forcing eye contact, scripting social interactions — which makes the traditional checklist of "autism signs" harder to spot. But masking isn't the whole story. The diagnostic tools themselves carry bias. They were built on observations of autistic boys, so they look for patterns that show up more visibly in boys. A girl who would eventually receive an autism diagnosis had less than a one-in-three chance of getting that diagnosis before age 10, according to patient advocate Anne Cary.
Dr Judith Brown of the National Autistic Society frames it as a historical blind spot: "Historically, it was wrongly assumed that autistic people were mostly men and boys, but we now know that women and girls are more likely to 'mask' what traditionally thought of as signs of autism, making it harder to identify the challenges they face."
The real cost isn't statistical. It's the girl who spent a decade thinking she was lazy, rude, or broken. It's the teenager whose anxiety spiraled without anyone connecting it to unmet sensory needs. It's the young woman who reached crisis point with her mental health because the support system never knew to look for her.
What Comes Next
Psychiatrists are already seeing the shift — more women and girls are coming forward for assessments as awareness spreads. That's progress, but it's also a warning: diagnostic services need to catch up. Jolanta Lasota, chief executive of Ambitious about Autism, is direct about what's required: "It is crucial researchers and diagnostic services continue to build understanding of the different presentations of autism in girls and women, and that our support services adapt to accommodate the increasing number of people who we now know need them."
The study doesn't just reveal a gap in diagnosis. It reveals a gap in how we've been looking.
