About 1-2 people of every 1,000 have autism . Most recent reviews tend to estimate a prevalence of 1 â `` 2 per 1,000 for autism and close to 6 per 1,000 for ASD ; because of inadequate data , these numbers may underestimate ASD 's true prevalence . PDD-NOS 's prevalence has been estimated at 3.7 per 1,000 , Asperger syndrome at roughly 0.6 per 1,000 , and childhood disintegrative disorder at 0.02 per 1,000 .