In countries such as the United States, about 6 in 1,000 children have autism.^{1 2 3}

About 1 in 100 children may have any type of autism spectrum disorder (a group of conditions that includes autism, Asperger's syndrome and other similar conditions).³

Autism affects about four times as many boys as girls.⁴ And it happens in children from all ethnic backgrounds and in people in all countries around the world.

Doctors once thought autism was rare. But newer studies show it seems to be getting more common. It's hard to say why. This may be just because the newer studies have been better at finding children with autism. Or it may be because the way doctors define autism has gotten wider. We need more research before we can say for sure what's causing the increase in autism.²