In the US, four out of five people with an autism diagnosis are male. There is not broad consensus on exactly why such a sex disparity exists, how much is due to underdiagnosis in girls and women, versus a genuinely higher frequency in boys and men.
Some scientists are looking for neurological and genetic differences that may cause autism to present differently in girls and women. Meanwhile others are considering social factors that may account for the gap.
In a study of children displaying similar symptoms of autism, girls were much less likely to have a formal diagnosis than boys, and girls were diagnosed at older ages. Another study suggested that autistic girls have fewer “special interest” habits than autistic boys, however clinicians argue that it’s more likely current diagnostic criteria is biased to catch typically male-coded interests (like dinosaurs and trains) more than typically female-coded interests (like makeup and pop music).
Autism researcher Brenda Myles says gender biased socialization contributes to underdiagnosis.
“We overtly teach social skills to girls,” They are told not to get angry, they are told to be nice, they are told to share — all of those behaviors.”
The next time someone tells you there are more autistic boys than girls, ask them why they think that is.
Angie's Anti-Theistic Thoughts 
A large part of it is that the existing literature essentially assumed that Kanner’s observed frequency of about 4/5 male, 1/5 female was accurate, so then future studies were designed to maintain that ratio. And then when they built diagnostic criteria, and they standardized them on how well they maintain the ratio. And repeat, year on year, where at every step, they’ve been assuming 80% male as a distribution and validating everything by how well it reproduces 80% and then turning around and pointing at the stuff designed to reproduce a ratio of 80% and saying because it produces the ratio of 80%, there’s an actual genetic difference in frequency at play.
And you know what? There might be. But I’m not convinced because they haven’t established yet that the 80% ratio is an actual phenomenon of autism or an artifact of designing their diagnostic criteria so that it produces a 80% gender split.
In any event, when it comes to the gender distribution of autism diagnoses, I have rarely seen a more textbook example of circular reasoning in science.