MMWR Surveillance Summaries; March 30, 2012 / Vol. 61 / No. SS–3
Prevalence of Autism Spectrum Disorders — Autism and Developmental Disabilities Monitoring Network, 14 Sites, United States, 2008
This report provides updated autism spectrum disorder (ASD) prevalence estimates from the 2008 surveillance year, representing 14 Autism and Developmental Disabilities Monitoring (ADDM) sites in the United States. For 2008, the overall estimated prevalence of ASDs among the 14 ADDM sites was 11.3 per 1,000 (one in 88) children aged 8 years who were living in these communities during 2008. The extent to which these increases reflect better case ascertainment as a result of increases in awareness and access to services or true increases in prevalence of ASD symptoms is not known.

http://www.cdc.gov/mmwr/pdf/ss/ss6103.pdf