Is Autism Really More Common in Boys? A Study Says No

A large study in Sweden showed that the difference between men and women in autism diagnosis decreases with age. Many girls are diagnosed later, suggesting that autism may be equally common in both sexes. This points to failures in the early recognition of ASD in women.

Autism spectrum disorder, known as ASD, is a brain development condition that accompanies a person from childhood. It is mainly linked to differences in social communication, very specific interests, and repetitive behaviors.

Over the last few decades, the number of autism diagnoses has increased significantly in several countries, especially since the 2000s, which has drawn the attention of researchers and healthcare professionals.

Currently, it is estimated that between one and three in every hundred people have a diagnosis of ASD in the United States and Western Europe. For a long time, it was believed that autism was much more common in boys than in girls.

This difference between the sexes has led to the emergence of several theories to explain it, including the idea that women have some kind of "biological protection" or that men exhibit greater genetic variation linked to autism.

Other explanations point to social and behavioral factors. Many girls, for example, learn from an early age to imitate social behaviors, hide difficulties, and adapt better to social expectations. This phenomenon is known as "camouflage" and can cause signs of autism to go unnoticed. Furthermore, symptoms in girls can be confused with other problems, such as anxiety or depression, delaying or even preventing a correct diagnosis.

Although autism is present from the first years of life, it is not always identified early. In some countries, such as Sweden, assessments during the preschool period help in diagnosis, but even so, many people only receive a diagnosis in adolescence or adulthood.

Changes in medical criteria over time have also contributed to the increase in diagnoses, as the concept of "spectrum" has come to include a wider range of characteristics and levels of support.

Social factors also influence these numbers. The age of parents at the time of their children's birth has increased in recent decades, and this may impact diagnosis rates across generations. These combined effects, age at diagnosis, changes in medical criteria, and generational differences, make the autism landscape more complex than it first appears.

To better understand these changes, researchers analyzed data from nearly three million children born in Sweden between 1985 and 2020. The study followed these individuals over time and observed when and how ASD diagnoses were made, taking into account age, sex, and year of birth. This type of analysis was only possible thanks to the country's detailed medical records and public health system.

The results showed something surprising: the difference between boys and girls decreases as the age at diagnosis increases. While boys tend to be diagnosed earlier, many girls receive the diagnosis only in adolescence or early adulthood. Over time, this gender difference practically disappears, reaching very close to equality in adulthood.

These findings indicate that autism may not be as common in males as previously believed. Instead, many girls and women may be being diagnosed too late. This reinforces the need to improve diagnostic criteria, raise awareness of how autism manifests in different people, and ensure that girls and women have faster access to appropriate assessments and support.

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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, Donald O Schnuck, Alexander Kolevzon, Natasha Marrus, Kristina Tedroff, Tychele N Turner, Lauren A Weiss, Benjamin H K Yip, Weiyao Yin, and Sven Sandin

BMJ. 392: e084164, 04 February 2026

doi: https://doi.org/10.1136/bmj-2025-084164

Abstract:

To examine changes in the male to female ratio in diagnoses of autism spectrum disorder (ASD) over a 35 year period, providing temporal trends in diagnosis (incidence rate), the male to female ratio, and the age-cohort specific cumulative male to female ratio (cMFR). Population based, prospectively collected birth cohort study. Participants 2 756 779 liveborn children recorded in the Swedish medical birth register between 1985 and 2020. Main outcome measure Age-period cohort analysis investigating associations between ASD and age at diagnosis, calendar period, birth cohort, and sex, quantified by incidence rate ratios and associated two sided 95% confidence intervals. Among 2 756 779 individuals born in Sweden between 1985 and 2020, ASD was diagnosed in 78 522 (2.8%) by the end of follow-up (2022). The incidence rate for ASD increased with each five year age interval throughout childhood, peaking at 645.5 (per 100 000 person years) for the male cohort at age 10-14 years and 602.6 for the female cohort at age 15-19 years in 2020-2022, and then decreased. Age specific incidence of ASD increased for each calendar period and birth cohort between 1985 and 2020. The male to female ratio decreased with increasing age at diagnosis and, for those older than 10 years, by calendar period. For the final year of follow-up in 2022, the cumulative male to female ratio for incidence of ASD was 1.2 by age 20 years. Further projection of these trends suggested that the cumulative male to female ratio would reach parity at age 20 years by 2024. 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.