Scientists in Sweden did a huge study about autism. They looked at almost 3 million people over many years.
For a long time, people thought autism mostly happened in boys. But this study found something different. While more boys get diagnosed when they are young, more and more girls get diagnosed as teenagers. By age 20, boys and girls are diagnosed at almost the same rate.
Why were girls missed? The signs of autism can look different in girls. Girls are often better at hiding their difficulties in social situations, so doctors might not notice. The study suggests we need better ways to spot autism in girls so they can get help earlier.