A new study suggests that autism may be just as common among girls as it is among boys, although girls are often diagnosed significantly later.

Changing Perceptions of Autism Prevalence

For a long time, it was believed that autism primarily affected males. However, a large Swedish study published in The BMJ indicates that the prevalence of autism among men and women may be roughly the same.

Diagnostic Challenges in Girls

Researchers identified a clear trend: girls begin to close the diagnostic gap with boys during adolescence. This highlights the need to understand why women are often diagnosed with autism later than men.

Rising Diagnoses and Gender Disparity

Over the past 30 years, the prevalence of autism spectrum disorders (ASD) has steadily increased. During this time, men were diagnosed about four times more often than women. Experts attribute the overall rise in diagnoses to broader diagnostic criteria and social factors such as parental age. It was thought that girls have better social and communication skills, making autism harder to detect. However, until now, there have been no large-scale studies tracking these trends across different life stages.

Scope of the Study

To address this gap, researchers analyzed national medical data on 2.7 million people born in Sweden between 1985 and 2022. Participants were followed from birth up to age 37.

Over more than 35 years of observation, autism was diagnosed in 78,522 individuals, representing 2.8% of the studied population. The average age at diagnosis was 14.3 years.

Age Peaks in Diagnosis

The rate of autism diagnoses increased with each five-year age group during childhood. For boys, the peak occurred at ages 10–14 (645.5 per 100,000 person-years), while for girls, it was at ages 15–19 (602.6 per 100,000 person-years).

While boys were more often diagnosed in childhood, there was a significant rise in diagnoses among girls during adolescence. By age 20, the ratio of boys to girls diagnosed with autism approached 1:1.

Study Limitations

The authors note that the study was observational and did not account for other conditions often associated with autism, such as ADHD and intellectual disability. It was also not possible to fully adjust for the influence of general genetic or environmental factors, including parental mental health.

Nevertheless, the scale and duration of the study allowed researchers to analyze data from the entire population and separate the effects of age, calendar period, and birth cohort.

Conclusions and Implications for Diagnosis

Based on their analysis, the authors write: “These data indicate that the male-to-female ratio in autism diagnoses decreases over time and with increasing age at diagnosis. This ratio may be significantly lower than previously thought and may not differ in adulthood in Sweden.”

The researchers emphasize the need to study why women receive an autism diagnosis later than men.

Perspectives from Patients and Experts

The findings are consistent with recent studies showing that autism in women is often missed or diagnosed much later. In an accompanying editorial, patient and patient rights advocate Ann Carey noted that the results confirm concerns about gaps in current diagnostic practices.

She stressed that such research helps challenge the long-held belief that autism is more common in men. However, Carey also warned that while women with autism wait for an accurate diagnosis, they are often mistakenly given psychiatric diagnoses—especially mood and personality disorders—and must advocate for recognition and appropriate treatment as autistic patients, just as their male peers do.