Why does autism seem easy to spot in boys during childhood, yet many women speak about receiving a diagnosis much later in life? A large study from Sweden offers a clear answer. Autism does not appear less often in girls – it often gets recognized later.
For decades, autism spectrum disorder has been linked more strongly with male individuals. Many reports showed about four male diagnoses for every female diagnosis.
That gap shaped public thinking, school screening, and even medical training. New evidence from Karolinska Institutet now shows that the gap shrinks with age and almost disappears by adulthood.
Autism diagnosis varies by gender
Autism spectrum disorder affects social interaction, communication, and behavior. Diagnosis rates have increased steadily over the past thirty years.
Broader diagnostic criteria, better awareness, and social changes such as older parental age have contributed to this rise.
Despite rising numbers, one pattern stayed constant for a long time. Childhood diagnosis favored boys. Girls often appeared missing from statistics. Many experts assumed autism occurred less often among female individuals.
The Swedish study challenges that belief by following people across childhood, teenage years, and adulthood.
Researchers used national health registers in Sweden to track autism diagnoses over time. The study included 2.7 million individuals born between 1985 and 2020.
Medical records followed each person from early childhood up to 37 years of age. Such a large dataset allowed researchers to study how age, birth year, and calendar time shape autism diagnosis.
Rates of autism diagnosis
Autism was diagnosed in about 2.8 percent of the study population. The average age at diagnosis was 14.3 years. Diagnosis rates increased through childhood for both sexes, but timing differed.
Male individuals most often received diagnoses between ages 10 and 14. Female individuals reached peak diagnosis rates later, between ages 15 and 19.
During early childhood, autism appeared far more common in boys. During adolescence, diagnosis among girls rose sharply.
By around age 20, the male to female ratio moved close to one to one. Autism did not suddenly appear during teenage years for girls. Recognition simply arrived later.
Researchers described this pattern as a female catch-up effect. Autism traits became harder to ignore as social demands increased during teenage years.
Autistic traits unfold over time
Several explanations help clarify delayed diagnosis among female individuals. Many girls develop strong coping skills at an early age. Social imitation, quiet behavior, and rule following can mask autistic traits in classrooms.
Diagnostic tools also play a role. Many assessment methods focus on behaviors more commonly seen in boys.
Repetitive actions or visible social difficulties often trigger early referrals. Subtle communication struggles may escape attention for years.
Biology may also contribute. Some scientists describe a female protective effect, suggesting that girls require a higher genetic load before autistic traits become noticeable.
Other research points to differences in how traits unfold across development rather than outright protection.
Age, time, and birth year matter
The Swedish study separated three forces shaping diagnosis. Age at diagnosis explained why recognition shifts during teenage years.
Calendar period captured rising awareness and expanded diagnostic criteria. Birth cohort reflected changes across generations.
By separating these effects, researchers showed that sex differences shrink steadily with age. Childhood statistics exaggerate male dominance. Adult data tell a different story.
“These findings indicate that the male to female ratio for autism has decreased over time and with increasing age at diagnosis,” noted the researchers behind the study.
“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.”
Women misdiagnosed with depression
Late diagnosis often comes with consequences. Many women receive mental health diagnoses years before autism recognition. Anxiety, depression, and personality disorders often appear first in medical records.
Anne Cary, a patient and patient advocate, addressed this issue in a linked editorial. Cary explained that delayed recognition forces autistic women to push for appropriate care.
Cary wrote that autistic female individuals are often “(mis)diagnosed with psychiatric conditions, especially mood and personality disorders, and they are forced to self advocate to be seen and treated appropriately: as autistic patients, just as autistic as their male counterparts.”
Autism doesn’t favor boys
The Swedish study reshapes how autism prevalence gets interpreted. Early childhood data alone cannot describe lifetime patterns. Autism affects male and female individuals at similar rates by adulthood, at least within Sweden.
Improved screening that considers sex differences could help earlier recognition. Teachers, clinicians, and families may need broader definitions of autistic traits to avoid missed diagnoses.
Autism does not belong to one sex. Timing, awareness, and expectations shape who receives a label and when. Studies like this move understanding closer to reality rather than assumption.
The study is published in the journal The BMJ.