For decades, autism spectrum disorder, or ASD, has been widely described as a predominantly male condition. Medical textbooks, diagnostic manuals, and public health messaging have frequently cited a male-to-female diagnosis ratio of around 4:1. This figure has shaped research priorities, screening tools, and clinical expectations worldwide.
However, a major new population-based study published in The BMJ in February 2026 challenges this long-standing assumption. Using more than 35 years of Swedish national health data and following nearly 2.8 million individuals from birth into adulthood, researchers found that the male-to-female ratio in autism diagnoses steadily decreases with age. By early adulthood, autism diagnosis rates in males and females are nearly equal.
These findings suggest that autism may occur at similar rates across sexes, and that many girls and women are diagnosed later in life, if at all. The implications for clinical practice, research, and public health policy are profound.
The study, led by Caroline Fyfe and colleagues, analyzed prospectively collected data from the Swedish Medical Birth Register and the Swedish National Patient Register. The cohort included all children born in Sweden between 1985 and 2020 whose parents were also born in Sweden, totaling 2,756,779 individuals.
Autism diagnoses were tracked from age two through the end of follow-up in 2022. Unlike many previous studies, the researchers were able to disentangle three overlapping influences that affect diagnosis rates:
This age-period-cohort modeling allowed the team to examine not just how many people were diagnosed, but when and under what diagnostic conditions those diagnoses occurred.
One of the most striking findings is the scale of increase in autism diagnoses over time. Between the early 1990s and 2022, autism incidence rose approximately tenfold across most age groups.
For example, among children aged 10 to 14 years, diagnosis rates increased from roughly 56 per 100,000 person-years in 2000 to more than 560 per 100,000 person-years by 2022.
This increase affected both males and females and is consistent with trends observed in other high-income countries. Factors likely contributing include expanded diagnostic criteria, increased awareness, better access to services, and greater recognition of autism across the lifespan.
While autism diagnoses remain more common in boys during early childhood, the sex gap narrows substantially with age.
Key findings include:
In practical terms, this means that many girls who will eventually be diagnosed with autism are simply diagnosed later than boys. The traditional childhood sex ratio therefore does not reflect lifetime autism incidence.
The study does not claim that biology plays no role in sex differences related to autism. Instead, it highlights that diagnostic timing and recognition differ substantially between males and females.
Several mechanisms likely contribute.
Autistic girls often display fewer overt repetitive behaviors and may show stronger social imitation skills in childhood. Language development may appear less delayed, and social difficulties can be more subtle during early years.
Standard diagnostic tools were largely developed and validated using predominantly male samples. As a result, they may be less sensitive to female presentations of autism.
Many autistic girls and women consciously or unconsciously mask their autistic traits by mimicking peers, rehearsing social scripts, or suppressing behaviors considered socially unacceptable.
This masking can delay detection until adolescence or adulthood, when social demands increase and coping strategies become harder to sustain.
Girls and women with autism are more likely to receive earlier diagnoses of anxiety disorders, depression, eating disorders, or personality disorders. These diagnoses may obscure underlying autistic traits, delaying or preventing autism recognition.
Several studies have shown that women are more likely than men to receive psychiatric diagnoses prior to an autism diagnosis.
In Sweden, early childhood developmental screening is nearly universal. Children who do not raise early concerns may only come to clinical attention later, often through mental health services.
Women are generally more likely to seek healthcare for mental health concerns, which may partly explain the rise in autism diagnoses among adolescent and adult females.
Historically, higher male prevalence has been interpreted as evidence of a female protective effect, meaning that females require a greater genetic burden to manifest autism.
While this hypothesis remains under investigation, the near-parity of lifetime diagnosis rates observed in this study challenges the idea that large biological differences alone explain sex disparities.
If females are diagnosed later rather than less often, diagnostic bias and social factors may account for a significant portion of the observed sex ratio.
These findings carry important messages for healthcare professionals.
First, autism should not be considered unlikely in adolescent and adult women, particularly those with long histories of anxiety, depression, eating disorders, or treatment-resistant psychiatric symptoms.
Second, clinicians should be aware that traditional screening tools may under-identify autism in females and that collateral histories and qualitative assessments are especially important.
Third, delayed diagnosis can have serious consequences. Many autistic women report years of inappropriate treatment, misunderstanding, and lack of access to appropriate supports before receiving an autism diagnosis.
This study underscores the need for:
Importantly, it also suggests that commonly cited prevalence figures based on childhood data may systematically underestimate autism in females.
The idea that autism is overwhelmingly male has shaped both scientific understanding and social perception for decades. This new evidence suggests that the narrative needs updating.
Autism may not be less common in girls and women, but less commonly recognized early in life. As diagnostic practices evolve and awareness grows, reported sex ratios are likely to continue moving toward parity.
Recognizing this shift is not merely an academic exercise. It has real consequences for diagnosis, care, and quality of life for millions of autistic women worldwide.
Fyfe C, Winell H, Dougherty J, et al. Time trends in the male-to-female ratio for autism incidence: population-based, prospectively collected, birth cohort study.
BMJ. 2026;392:e084164. DOI: 10.1136/bmj-2025-084164
Cary AE. Towards the equal recognition of autism in girls and women.
BMJ. 2026;392:s120.
This article is for informational and educational purposes only and does not constitute medical advice. It is not intended to diagnose, treat, cure, or prevent any condition. Readers should consult qualified healthcare professionals for individual assessment, diagnosis, or treatment decisions.
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