A quarterly publication of the Autism Research Institute
Winter 2026 | Number 1, Volume 40
The male-to-female ratio for autism spectrum disorder (ASD) diagnoses is traditionally considered to be 4:1, but researchers in Sweden report that males and females actually have comparable rates of autism spectrum disorders due to a female “catch-up” effect during adolescence.
Caroline Fyfe and colleagues used national registers to determine diagnosis rates of autism for 2.7 million people born in Sweden between 1985 and 2022, limiting the study population to people whose parents were both born in Sweden. Of this group, 78,522 received an autism diagnosis, with rates of ASD diagnoses increasing about 10-fold over the study period and the male-to-female ratio decreasing over time.
By the final year of their follow-up in 2022, Fyfe and colleagues say, “the cumulative male-to-female ratio for incidence of ASD was 1.2 by age 20 years.” This male-to-female ratio, they say, “may therefore be substantially lower than previously thought, to the extent that, in Sweden, it may no longer be distinguishable by adulthood.”
The researchers found that cumulative rates of autism diagnoses rose at each five-year interval during childhood. For males, the rate peaked between 10 and 14 years of age; for females, it peaked between 15 and 19 years of age. Males were more likely to receive a diagnosis during childhood, while female diagnoses increased during adolescence. By the final year of follow-up in 2022, the researchers say, “the cumulative male-to-female ratio for incidence of ASD was 1.2 by age 20 years.”
They conclude, “Findings indicate that the male-to-female ratio for ASD has decreased over time and with increasing age at diagnosis. This male-to-female ratio may therefore be substantially lower than previously thought, to the extent that, in Sweden, it may no longer be distinguishable by adulthood. This finding highlights a need to investigate why girls and women receive diagnoses of ASD later than boys and men.”
Patient advocate Anne E. Cary says, “This evidence seems to support the argument that systemic biases in diagnosis, rather than a true gap in incidence, underlie the commonly accepted 4:1 male-to-female ratio.” She adds that while the onset of autistic traits may be delayed in females, making early identification less likely, it is also possible that “the assessment tools contain sex biases and need reworking.”
She adds, “Studies like that of Fyfe and colleagues are essential to changing the assumption that autism is more prevalent in the male sex than in the female sex. As autistic girls and women await proper diagnosis, they are likely to be (mis)diagnosed with psychiatric conditions, especially mood and personality disorders, and they are forced to self-advocate to be seen and treated appropriately: as autistic patients, just as autistic as their male counterparts.”
“Time trends in the male to female ratio for autism incidence: population based, prospectively collected, birth cohort study,” Caroline Fyfe, Henric Winell, Joseph Dougherty, David H. Gutmann, Alexander Kolevzon, Natasha Marrus, Kristina Tedroff, Tychele N. Turner, Lauren A. Weiss, Benjamin H K Yip, Weiyao Yin, and Sven Sandin, British Medical Journal, December 9, 2025 (free online). Address: Caroline Fyfe, [email protected].
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“Towards the equal recognition of autism in girls and women,” Anne E. Cary, British Medical Journal, February 4, 2026 (free online). Address: Anne E. Cary, [email protected].
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“Rates of autism in girls and boys may be more equal than previously thought,” news release, British Medical Journal, February 4, 2026.
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“Everyone thought autism mostly affected boys. This study says otherwise,” news release, BMJ Group, February 10, 2026.
