Autism in Girls Often Goes Undiagnosed

Quick: Picture a person with autism. Did you picture a young boy or an adolescent male? Chances are many of you did. What you probably didn’t imagine in your head is a little girl or young woman. In fact, for decades, health care professionals, teachers and the general public thought autism was a male-only condition, that females simply weren’t affected by it. Some still believe that.

However, more recent research—and new diagnoses and personal stories—now show autism can affect both males and females.

In a 2026 study, researchers in Sweden examined autism spectrum disorder (ASD) diagnoses for babies born in Sweden between 1985 and 2020. By 2022, 78,522 kids had been diagnosed with ASD. The rate of diagnosis increased as kids got older, with females tending to receive a diagnosis later. The diagnosis rate peaked for males in the 10–14 age group and for females in the 15–19 age group.

After those peaks, diagnosis rates dropped for each of those age groups. By the final year of the study in 2022, among diagnosed individuals who had reached age 20, the male to female ratio for incidence of ASD was only 1.2. Researchers projected that by 2024, the diagnosis rate for those who had reached age 20 would be equal for both males and females.

Rates of autism have been increasing in the U.S., but that’s likely due to increased screening and diagnosis and a broadened definition of ASD. In the latest “Diagnostic and Statistical Manual of Mental Disorders” (DSM) the definition of “autism” was broadened to “autism spectrum disorder.” The new definition also eliminated the requirement that autism symptoms had to be present before age 3—if girls are diagnosed later, they wouldn’t have met that requirement. In addition, DSM no longer uses diagnoses like Asperger’s syndrome, which is now considered a part of ASD instead.

Research in Autistic Girls

An ongoing study in the U.S. called Girls with Autism-Imaging of Neurodevelopment (GAIN) has been studying girls with autism for the past 12 years. Nearly 100 autistic females have been enrolled at ages 2 to 4. They are followed through early childhood, as researchers examine potential differences in the brains of autistic females versus autistic males.

Christine Wu Nordahl, PhD, started the GAIN study after working on another study called the Autism Phenome Project (APP) that looks at similarities and differences among different groups of autistic kids. As she worked on that study soon after earning her PhD, it was clear that most of the participants in the study were boys. Dr. Nordahl, now a professor and neuroscientist in the Department of Psychiatry and Behavioral Sciences at the University of California, Davis, sought out and obtained grant funding to launch GAIN to increase the number of girls in the APP, as well as to study any differences between autistic boys and girls.

“I have talked to a lot of parents about their girls who were being told by their clinicians, their pediatricians, ‘Oh, autism doesn’t happen in girls.’”

While more is known now about girls with autism, there’s still a misunderstanding and stigma that autism is rare—or nonexistent—in girls. “I have talked to a lot of parents about their girls who were being told by their clinicians, their pediatricians, ‘Oh, autism doesn’t happen in girls. It can’t be autism. It must be something else,’” Dr. Nordahl said. “That actually still happens now, but probably to a lesser degree.”

Dr. Nordahl shared a personal story of a friend who was trying to get a proper diagnosis for her daughter. The friend was smart, had the money and resources to seek out various specialists, lived in a large U.S. city where specialists were available, visited prestigious medical facilities. And yet, her daughter wasn’t diagnosed with autism until age 10. She had even been screened for autism multiple times, but clinicians kept diagnosing conditions such as anxiety and obsessive-compulsive disorder.

“This was very personal to me because this was my close friend and I hadn’t been able to help her daughter get a diagnosis sooner,” Dr. Nordahl said. “So, while things have gotten better, we still have a long way to go.”

In examining brain structure and function, the GAIN study has discovered numerous differences between male and female autistic brains. In fact, Dr. Nordahl said, “One of the things that has struck me in 10 years of looking for sex differences in the brain is that—in almost every study that we do where we set out to look for sex differences in the brain—we find them, and some of them are more widespread than we would expect. What’s puzzling about this is that we don’t see behavioral differences in our boys versus girls.”

In a recent study examining the cortex, or the outer layer of the brain, Dr. Nordahl expected to find similarities between the sexes. Instead, she said, “I was frankly surprised at how many differences we saw across development. Interestingly, those differences don’t seem to be leading to big, overt differences in behavior, which shows that you can have two different paths to get to the same place. But knowing how and when these paths differ can help us figure out what types of interventions may be most effective at certain periods of development.”

The cortex, or gray matter, contains all of the brain’s neurons, and the thickness of the cortex changes across development. As toddlers get older, the cortex gets thinner, which likely reflects refinement in the connections neurons are making with other parts of the brain—a process called synaptic pruning.

The research team is also studying other aspects of brain development, including how white matter tracts, or the connections between neurons change, as well as specific structures deep within the brain such as the amygdala and basal ganglia. The goal is to understand how brain development may predict behavioral outcomes and co-occurring conditions such as attention-deficit hyperactivity disorder and anxiety.    

The Trauma of Autistic Masking

It may seem surprising that the GAIN study hasn’t uncovered behavioral differences between males and females with autism since there is a difference in how autistic boys and girls are diagnosed and perceived. But are these inherent differences—or are these societal expectations and gender stereotypes of how boys and girls are “supposed” to act?

Overall, girls develop language and fine motor skills earlier. Combine that with society’s tendency to write off any challenging boy behavior as “boys will be boys,” while girls are expected to be more docile and well-behaved, Dr. Nordahl pointed out.

You might think that would lead to girls not fitting into those norms to actually be diagnosed earlier. Instead, many female children and teenagers tend to “mask” their symptoms, which could be stressful and lead to anxiety, depression, imposter syndrome and other challenges.

It can also lead to loneliness. In Dr. Nordahl’s work with neurodivergent teenagers, she finds girls care much more about making friends and being a part of a group than boys tend to.

“Masking can come at this cost of increased anxiety or depression, or a depletion in their social battery, burnout and meltdowns,” she said. “Having more awareness that this is happening and that it can happen more in autistic females is really important.”

Anne E. Cary knows this all too well. Now 42, Cary wasn’t diagnosed with autism until she was 34. Her adolescence and early adulthood was filled with mental health misdiagnoses.

“The signs of my autism … were what I learned to be ashamed of, and I learned that they needed to be kept private.”

“My diagnoses of depression and anxiety didn’t seem sufficient to explain how different I felt from other people,” Cary said. In fact, she now believes depression and anxiety were symptoms not of her autism but of the pressure and trauma to mask her autism.

Cary said she might have been diagnosed earlier if she hadn’t grown up in the South, where she was expected to be a sweet Southern girl who displayed social graces. Plus, with professors as parents, she felt extra pressure to excel academically.

“I learned that what mattered to people was the maintenance of those performance levels, and most things did feel performative,” she said. “The signs of my autism … were what I learned to be ashamed of, and I learned that they needed to be kept private.”

Cary would secretly cry in her room because she couldn’t sustain friendships. She tried to hide her love for memorizing world records and swim times. She was ashamed that, although she was smart in school, she couldn’t seem to keep her room cleaned or learn how to scramble an egg.

“I think that that shame is more commonly inflicted on girls in all sorts of different ways, and if I hadn’t been so ashamed of my autistic traits, I might have been more authentically myself and more authentically autistic in public, and I might have been diagnosed earlier.”

Calling her masking and accompanying shame “trauma” is not an overstatement, Cary said. “Feeling as if there’s something inherently flawed with being oneself in public spaces is a traumatic experience.”

While working as a special education teacher 10 or so years ago, she realized she related to her autistic students, who seemed to “baffle” the other teachers. She sought out an autism evaluation at her local mental health clinic—and after two years on the wait list to be seen—she was finally diagnosed with autism.

“I was thrilled. It explained so much of my past,” she said. She sought out Facebook groups for autistic adults, especially autistic women, where she quickly found a community and became involved in autism activism. This year, she was asked to write the editorial that accompanies the Swedish study in The BMJ. Her editorial calls out the harms from the crisis of underdiagnosis and misdiagnosis of autism in females.

“Pretty universally, the women I interacted with in these groups were diagnosed in adulthood,” Cary said. “There are a lot of groups just for autistic women and nonbinary folks because our experience is very different from growing up with that diagnosis.

“What makes autism disabling is a lack of accommodation. So, diagnosis is thus enabling,” Cary said.

If clinicians are informed that autism may be as likely a diagnosis for females as for males, they’ll be more likely to consider it as a potential diagnosis in their female patients, she said. “And those diagnoses will help autistic girls and women understand themselves, find community and participate more fully in society, knowing what supports they need.”