The incidence of autism is similar in boys and girls, although boys are diagnosed earlier

Autism rates in men and women may be comparable. The findings of a study conducted on a sample of 2.7 million people in Sweden over a 35 year period, and published this Thursday in the medical journal BMJ, suggest that the male to female ratio of Autism Spectrum Disorder (ASD) has decreased over time. In early childhood, before the age of 10, the male to female ratio is 3:1 (the most widely accepted ratio a few years ago was 4:1). But the numbers balance out over time. By age 20, the rate of diagnoses is practically balanced. “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,” the authors conclude.

The analysis included a sample of more than 2.7 million people born in Sweden between 1985 and 2020, followed from birth to a maximum age of 37. More than 78,000 received a ASD diagnosis. The detection of this disorder increased with age throughout childhood, peaking for boys between the ages of 10 and 14 and for girls between 15 and 19. The authors do not address the question that experts have been asking for years: why girls get diagnosed later.

“The study rests on a solid foundation, both because of the track record of the teams that authored it and the quality of the Swedish registry system,” explains Jorge Aguado, a clinical psychologist at the Hospital Clínic and a researcher at the University of Barcelona. Speaking to the scientific website SMC, the expert also points out some limitations: “Its conclusions can only be considered fully generalizable to the Swedish population, which is based on registered diagnoses (passive cases), reflecting, above all, detection patterns rather than true prevalence; and it does not incorporate comorbidities that could influence the age at diagnosis.” Even so, he gives it a positive assessment and emphasizes that the results remain in line with the most recent evidence.

Autism is more prevalent in boys than in girls, but the exact ratio has varied over the years. In 2012, the U.S. Centers for Disease Control and Prevention estimated that boys were 4.7 times more likely than girls to receive an autism diagnosis. By 2018, the ratio had decreased to 4.2 to 1. In 2023, the figure was 3.8 to 1. The most recent available data, from 2025, indicates that boys are 3.4 times more likely to be diagnosed. The gap continues to narrow.

In a review of dozens of studies conducted by the American Academy of Child Psychiatry, British researchers estimated that the actual ratio was closer to 3 to 1, identical to the ratio suggested by the Swedish study for infants. The authors then pointed to a possible reason for the underdiagnosis in girls: a gender bias in the criteria for detecting ASD, traditionally based on males.

Another reason that could explain this gender gap is the phenomenon of camouflage: girls with milder cases learn to mask their symptoms—by improving nonverbal communication, for example—in order to fit in socially. Gender roles could explain these differences. Girls are expected to smile more, to be more caring, more sociable, and less violent. They are raised to be that way, including autistic girls. And this gives them the tools to disguise their condition.

ASD is a neurodevelopmental disorder that has been extensively researched since the mid-20th century. It is estimated to affect approximately one in every 100 school-aged children. Studies suggest it is closely linked to genetics, but diagnostic tests are primarily observational. There is no single test or medical examination that definitively diagnoses autism, as one can diagnose celiac disease or Down syndrome. Clinical assessment is more subjective and subtle. This is why autism can be easily disguised, especially when it is not severe.

In the first study on autism, published in 1943 by Leo Kanner, a psychiatrist at Johns Hopkins University, he identified 11 children—eight boys and three girls—with “a strong desire for solitude and uniformity.” It was then described as a monolithic and unequivocal disease. Over the years and with further research, it has become clear that it is actually a spectrum with varying degrees. There are individuals with profound autism, unable to lead independent lives and integrate into society. And there are people with a less severe form who can lead perfectly normal lives.

This doesn’t mean that identifying them isn’t important. When someone is on the spectrum and hasn’t been diagnosed, they grapple with a certain amount of misunderstanding, not only from society but also from themselves. They don’t understand what’s happening to them. This would explain why many people diagnosed in adulthood often also struggle with mental health issues. It’s difficult to live with something that’s happening to you but doesn’t have a name. Studies like this one help better understand the particularities of a neurodevelopmental disorder that we still don’t fully understand. And they reflect that something is changing, at least in terms of its detection.

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