Why have girls historically been diagnosed with autism less often than boys?

For many years, autism was diagnosed far more often in boys than girls. Early studies often reported ratios of around four boys for every girl diagnosed, although more recent research suggests the true difference may be considerably smaller. Researchers increasingly believe that part of this gap reflects how autism has been understood, recognised and assessed over time.

The story of autism in girls is not simply a story about girls. It is also the story of how our understanding of autism has evolved. As research expanded beyond early, highly visible presentations, clinicians and researchers began recognising autistic girls and women who had always been there, but who did not fit traditional expectations.

Understanding the diagnostic gap means understanding the evolution of autism itself.

The question behind the numbers

For decades, autism was viewed as something that affected boys much more often than girls. Studies based on existing diagnoses often reported ratios of around 4:1, whilst more recent research suggests the gap may be closer to 3:1 and, in some populations, potentially smaller still. In the largest UK schools study, covering more than seven million pupils, 2.81% of boys held an autism diagnosis compared with 0.65% of girls. Researchers continue to debate the precise figures, but many agree that diagnostic rates alone may not tell the whole story. Community studies that actively assess children often identify more autistic girls than expected based on diagnosis rates alone.

This led researchers to ask an important question: are autistic girls genuinely rare, or have some simply been overlooked? To answer it, it helps to understand how autism itself has changed over the last fifty years.

A very different understanding of autism

If you had asked professionals about autism in the 1970s, you would probably have received a very different answer from the one you would hear today.

At that time, autism was often understood as a rare condition associated with children who had highly visible support needs and, frequently, co-occurring intellectual disability. Early prevalence estimates were often around 4-5 children per 10,000, roughly equivalent to around 1 in 2,000-2,500 children. Today, prevalence estimates are dramatically higher, with recent studies often suggesting around 1 in 30-40 children.

Researchers were not typically looking for children who were academically successful, socially motivated, verbally fluent or attending mainstream schools, and research samples were heavily male. None of this reflected poor science: researchers could only describe the people they had access to. The difficulty was that the people being recognised represented only part of the picture, and in many ways the history of autism research has been a history of discovering how much bigger that picture really was.

From a narrow category to a spectrum

Over subsequent decades, autism began to broaden. Researchers increasingly recognised autistic people who did not fit the earlier model. Some had fluent language. Some attended university. Some held jobs and relationships. Some presented with strengths and abilities that would not have been associated with autism in earlier decades.

At the same time, diagnostic frameworks evolved. Definitions became broader and increasingly reflected the diversity of autistic presentations rather than a narrow group of highly visible cases.

As understanding widened, prevalence estimates increased. Whilst no single factor explains rising prevalence, most researchers agree that broader diagnostic criteria, increased awareness, improved identification and recognition of previously overlooked groups have all contributed. Girls and women form an important part of that story.

As the spectrum widened, the question became difficult to ignore: if autism is broader than we previously thought, where are the girls?

The girls who didn’t match the picture

One of the challenges facing clinicians was that many girls did not resemble the traditional image of autism. People often expected autism to look a particular way, yet many girls were socially interested, appeared to have friendships, performed well academically or worked extremely hard to fit in. Because they did not always match existing expectations, autism was often considered later or not considered at all.

Importantly, this does not mean that professionals were deliberately ignoring girls. More often, it reflected the limitations of the reference picture that had developed over decades of research and clinical practice.

As researchers listened more closely to autistic girls and women, another pattern emerged. Many described spending years observing, analysing and consciously learning social behaviour. Rather than lacking interest in people, they were often highly interested in understanding them. This challenged long-standing assumptions about what autism was supposed to look like and helped drive new research into female presentation and camouflaging.

The discovery of masking

Perhaps one of the most significant developments in autism research has been the growing recognition of masking, sometimes called camouflaging. Researchers and autistic women themselves began describing a pattern in which social difficulties were not absent, but hidden. Some people consciously studied social situations, analysed friendships, copied behaviours and rehearsed conversations. Others learned over time which behaviours appeared socially acceptable and which attracted unwanted attention.

The result was that some autistic girls appeared to be coping in settings where referrals often begin, such as schools or clinics, despite investing enormous effort into maintaining that appearance. This shifted the focus of research: instead of asking “what does autism look like?”, researchers increasingly began asking “what is this person experiencing?”

For many girls, the most important aspects of their autism were not immediately visible. The effort required to navigate social situations, the exhaustion that followed, and the strategies used to fit in often became apparent only when researchers and clinicians explored lived experience in greater depth.

How research changed assessment

As understanding of autism evolved, assessment methods evolved too. Earlier questionnaires and screening tools were developed at a time when our understanding of autism was much narrower. As research into masking, female presentation and lived experience expanded, new approaches emerged.

Laura Hull and colleagues developed the Camouflaging Autistic Traits Questionnaire (CAT-Q) to explore masking, compensation and camouflaging strategies. Around the same time, Tony Attwood, Michelle Garnett and colleagues contributed to the development of the Girls Questionnaire for Autism Spectrum Condition (GQ-ASC), designed to explore experiences commonly reported by autistic girls and women. More recently, Michael English and colleagues developed the Comprehensive Autistic Trait Inventory (CATI), a measure that reflects contemporary understanding of autism by including areas such as sensory sensitivity, social camouflage and self-regulatory behaviours.

Importantly, these tools were not developed because autism in girls is entirely different. They were developed because researchers realised that some experiences had not been receiving enough attention.

Observational assessments such as the ADOS-2 remain valuable parts of many assessment pathways. However, there is growing recognition that no single tool can fully capture the diversity of autistic presentations. Modern assessment increasingly places emphasis on developmental history, lived experience, information from multiple settings and understanding the effort involved in navigating everyday life.

Diagnostic overshadowing and alternative explanations

Another important finding from research is that many girls who are eventually identified as autistic often receive other explanations first. Anxiety, perfectionism, friendship difficulties, eating difficulties, emotional regulation challenges or low mood may all be recognised and may all be genuine. However, these experiences do not necessarily explain everything.

Sometimes autism exists alongside those difficulties, and sometimes understanding autism helps explain why they developed in the first place. Researchers refer to this phenomenon as diagnostic overshadowing, where one explanation receives so much attention that other possibilities are explored less thoroughly. For some girls, this can contribute to years of partial explanations without anybody putting the whole picture together.

What have we learned?

Today’s understanding of autism would be almost unrecognisable to many professionals working fifty years ago. The field has moved from viewing autism as a rare condition affecting a small and highly visible group of children, to recognising a much broader neurodevelopmental spectrum that includes people with widely varying strengths, challenges and support needs, and alongside that shift has come growing recognition of autistic girls and women.

The diagnostic gap has not disappeared. Many girls are still identified later than boys, and some continue to be missed altogether. However, our understanding of female presentation, masking, sensory experiences and lived experience is considerably more developed than it was even twenty years ago, and research continues to evolve with our understanding growing alongside it.

What this means for families

Perhaps the most important lesson from this history is that autism cannot always be understood by looking only at what is immediately visible. The journey from early autism research to contemporary understanding has repeatedly shown that people’s experiences matter, and that behaviour alone rarely tells the whole story.

For some children, particularly girls, understanding autism may require looking beyond appearance, school reports or first impressions. It may involve understanding effort, uncertainty, sensory experiences, coping strategies and the differences between environments.

At The Neurodiversity Service, these ideas inform how we approach assessment. Our aim is not simply to determine whether autism is present, but to understand the person’s experiences, strengths, support needs and the context in which those experiences have developed.

In many ways, the history of autism is a story about widening our understanding of who autistic people are.

Girls were never absent from that story. For a long time, they simply sat outside the picture people were expecting to see.

Related reading: Autism in girls: masking, school and looking beyond the stereotypes

Coming soon: Why are autism rates increasing?

Frequently asked questions

Sources: Loomes, Hull and Mandy (2017), Journal of the American Academy of Child and Adolescent Psychiatry, meta-analysis of male-to-female autism ratios (≈3:1). Newcastle University and University of Cambridge analysis of the English school census, 7,047,238 pupils (2.81% of boys and 0.65% of girls holding an autism diagnosis). Lotter (1966), early epidemiology of autism (≈4.5 per 10,000). Hull et al., Camouflaging Autistic Traits Questionnaire (CAT-Q). Attwood, Garnett et al., Girls Questionnaire for Autism Spectrum Condition (GQ-ASC). English et al. (2021), Comprehensive Autistic Trait Inventory (CATI). This article is general information, not clinical advice for an individual situation.