Why autism is diagnosed later in females than males

By Dr. Sanchari Sinha Dutta, Ph.D.Reviewed by Lauren HardakerFeb 9 2026

Large-scale Swedish data reveal a female “catch-up” effect in autism diagnoses, reshaping how scientists understand sex differences in when, not whether, autism is identified.

Study: Time trends in the male to female ratio for autism incidence: population based, prospectively collected, birth cohort study. Image credit: Elenka Klimova/Shutterstock.com

A new study published in The BMJ points out that females are more likely to be diagnosed with autism spectrum disorder later in life than males.

Why girls’ autism symptoms are often missed early

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by repetitive behaviors, verbal communication difficulties, socialization difficulties, and restrictive interests. The prevalence of this condition has increased significantly since the early 2000s. According to the Centers for Disease Control and Prevention (CDC) data, the prevalence of ASD among 8-year-old children in the United States has increased from 0.7 % in 2002 to 3.3 % in 2022.

Over the past 30 years, the ratio of ASD diagnosis between males and females has mostly remained high, roughly at 4:1. Several theories have been put forward to explain this high male-to-female ratio for ASD diagnosis. Some theories indicate that females require a higher genetic burden than males for noticeable ASD-related behaviors, while others suggest that greater genetic variability in males may make them more likely to meet diagnostic thresholds for ASD.

The possibility of underdiagnosis or delayed diagnosis of ASD in females may be higher than in males, as girls and women typically have better social and communication skills that make symptom identification difficult. This may also contribute to the high male-to-female ratio for ASD diagnosis in childhood among females.

Despite several theories, direct population-level evidence explaining this imbalance has been largely absent. To fill this gap in the literature, researchers conducted a large-scale study in Sweden to examine temporal changes in ASD diagnosis rates among males and females over more than 35 years.

Registers track autism across decades

The research team used national registers to analyze ASD diagnosis rates among 2.76 million individuals born in Sweden between 1985 and 2020. Participants were followed up from birth to a maximum of 37 years, with follow-up extending to 2022.

Female diagnosis rates catch up during adolescence

The research team identified clinically diagnosed ASD in 2.8 % of participants over the 35-year follow-up period. The median age at diagnosis was 14.3 years.

Notably, the team found a shift in the diagnosis pattern with age. Specifically, the analysis revealed that the ASD diagnosis rate increased steadily with each five-year age interval throughout childhood. About a 10-fold increase in the ASD diagnosis rate was observed between 2000 and 2022, reflecting changes across calendar periods and birth cohorts, as well as evolving diagnostic practices over time.

Among males and females, the highest rates of diagnosis were observed in the 10–14- and 15–19-year age groups, respectively. The rates decreased afterwards for both males and females.

During the study follow-up period, the research team observed that males were more likely to be diagnosed with ASD in childhood, while females were more likely to be diagnosed during adolescence. This pattern resulted in a declining male-to-female ratio with increasing age, reaching approximately 1.2 by age 20 years in 2022, with statistical modelling projecting a cumulative male-to-female ratio of around 1.0 by around 2024.

A need for sex-sensitive diagnostic practices

The study provides valuable evidence that may refine the long-held belief that autism is more common among males than females. According to the findings, the well-known high male-to-female ratio for ASD diagnosis in childhood could be partly explained by the fact that females are more likely to be misdiagnosed or underdiagnosed with the disorder at younger ages. However, the ratio decreases substantially with increasing age, such that it may no longer be distinguishable by adulthood in Sweden.

The research team identifies a “catch-up” effect by the age of 20 years, when females are nearly as likely to have received an ASD diagnosis as males, based on cumulative incidence estimates and projections, suggesting a potentially similar lifetime rate of ASD diagnosis in both sexes within this population.

Several factors have been proposed in previous research to explain lower rates of ASD diagnosis in females during childhood. Females may exhibit greater biological, genetic, and developmental resilience that could make them less susceptible to earlier clinical identification of neurodevelopmental disorders like ASD.

Greater heritability has also been identified as a potential contributor to the higher prevalence of ASD in males. However, the study notes that higher heritability estimates in males may partly reflect non-genetic influences in females, including diagnostic ascertainment and differences in clinical presentation, rather than a strictly biological sex difference.

Another potential reason is that females are better than males at taking behavioral prompts from their peers, such as mimicking speech or expressions, leading to camouflaging of ASD-related traits and the resulting delay in detecting ASD-like behaviors.

The misattribution of symptoms to a previously identified psychiatric condition may also influence the age of ASD diagnosis and the variation in the male-to-female ratio by age at diagnosis. In this context, evidence indicates that almost 70 % of individuals with a diagnosis of ASD have at least one additional psychiatric condition and that women are more likely than men to have an earlier psychiatric diagnosis before an ASD diagnosis. These factors can potentially delay ASD diagnosis, especially in females.

Overall, the study findings highlight the need for investigating why females are diagnosed with ASD later in life than males. Future research in this field should consider the influence of other conditions linked to ASD, diagnostic practices, changes in diagnostic criteria over time, as well as shared genetic and environmental factors like parental mental health, for a more conclusive interpretation.

Download your PDF copy now!