While genetic risk factors are widely implicated in ASDs, the current increase in prevalence is not likely to result from genetic factors alone and it is possible that environmental factors may augment known genetic risks. In this study, researchers seek to examine if air pollution due to traffic, a common environmental exposure, increases risk for ASD. Using data collected as part of the Childhood Autism Risks from Genetics and the Environment Study (CHARGE), researchers will assess the role of traffic related air pollutants in autism risk based on monthly exposure at each child's home during prenatal, perinatal, and postnatal time points. Researchers will also examine genes that process pollutants in the body to determine if they are different in children with and without autism and to see if these genes interact with air pollution to increase autism risk. This work may provide important insight into what causes ASDs and evidence for risk due to a common environmental exposure (traffic-related air pollution).