Autism Probably Affects Boys And Girls Equally, Massive New Study RevealsNEWS | 05 February 2026Autism has historically been viewed as a condition that affects men and boys more frequently than women and girls. But a massive new study based on data from millions of people suggests this isn't actually the case, at least in Sweden.
While boys are diagnosed with the condition at higher rates during childhood, by adulthood, the ratio is roughly 1:1. This suggests it's not a case of fewer women having autism: it's just that they aren't diagnosed until later in life.
Autism spectrum disorder (ASD) diagnosis rates have been climbing since the 1990s, but diagnoses are not equal between males and females. The DSM-5, which defines mental health conditions and recommended treatments, states that for every four males diagnosed with autism, only one female receives a diagnosis.
But the recent study, led by medical epidemiologist Caroline Fyfe of the Karolinska Institute in Sweden, paints a very different picture, adding to a growing body of research that suggests autistic women and girls are being let down by current systems of diagnosis and treatment.
Autism is a neurodevelopmental disorder distinguished by difficulties in social interactions and communication, intense and specific interests in particular topics or activities, repetitive behaviors, and a strong preference for routine.
Treatment involves managing symptoms. It's a spectrum disorder, meaning some people require extra support – for instance, if they are unable to speak, earn an income, or live independently – while others can live independently and might be able to manage their symptoms with therapy, workplace accommodations, and by addressing specific symptoms and other health problems that often occur in tandem.
Diagnosis in childhood generally relies on the opinions of caregivers and healthcare professionals about whether the child's behaviors fit the DSM-5 description.
Of course, when a condition is defined as mostly affecting one demographic, it's easy to see why it may be overlooked in others, especially where symptoms present differently from what the DSM-5 describes, as some suspect they might.
"More recent research, as well as common self-reported experiences of autistic women, suggest that the true ratio is less skewed and that current practices are failing to recognize autism in many women until later in life, if at all," explains autism patient and advocate Anne Cary in an editorial accompanying the research.
"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."
Fyfe's team analyzed the medical records of more than 2.7 million Swedes born between 1985 and 2020 to track how clinical ASD diagnosis prevalence and ratios changed from birth up to 37 years of age.
While males were typically diagnosed with autism at much higher rates than females during childhood, this sex ratio leveled out to nearly equal by about age 20. That finding suggests autism isn't actually a predominantly male condition: it just takes longer for girls and women to be diagnosed. Why that is remains unclear.
"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," Fyfe and team report.
"These observations highlight the need to investigate why female groups receive diagnoses later than male individuals."
Related: There Are Critical Differences in The Brains of Girls Diagnosed With Autism
As Cary points out, it's possible that the data could be explained by a delay in the onset of autistic traits in females: "If that is the case," she writes, "it may be unreasonable to assume that autism is being missed in young girls."
But she also names a few good reasons why diagnostic oversight is a serious possibility.
"Firstly, sex differences are likely in the presentation of autistic traits, especially in childhood. Secondly, informers (e.g., parents, teachers) and diagnosticians might expect female individuals to be less likely to be autistic and develop a bias against recognizing autistic traits in girls," she explains.
The study's many years of data from such a large sample make the findings pretty robust, but some limitations need to be taken into account.
For one, the data is from an entirely Swedish-born cohort, so it may not represent what's going on in the rest of the world. It did not account for the effects of conditions that commonly occur alongside autism spectrum disorder, such as ADHD, intellectual disability, depression, and anxiety. It also didn't delve into other demographic factors, like race or socioeconomic status.
There was also a lack of outpatient data prior to 2001, which meant the age of ASD diagnosis was usually later for earlier cohorts in the study. This could mean the difference in age at diagnosis between males and females might actually be an underestimate.
There's clearly a lot more to learn about autism, particularly among women and girls.
"Further research should focus on phenotypic differences in how ASD manifests by sex and the implications for screening and diagnostic practices," Fyfe and team conclude.
The research was published in The BMJ.Author: Jess Cockerill. Source
