According to the US Centers for Disease Control, 1 in 110 American 8-year-olds has been diagnosed as autistic. (One in 70 boys and 1 in 315 girls.) This is up from another count made just a few years before that had the rate at 1 in 150.
Most of the increase is probably due to the expanding range of "autism spectrum disorder" and increasing awareness of autism. But at least some statisticians in the CDC seem to be worried that the prevalence of the disease may be increasing, too, and that would indeed be disturbing.