The report presents the findings of the Autism and Developmental Disabilities Monitoring (ADDM) Network, a population-based surveillance program, which aimed to determine the prevalence of autism spectrum disorders (ASDs) in children aged 8 years across six sites in the United States in 2000. The study used a multi-source, records-based approach to collect data from educational and health sources, with clinician review to confirm cases. The overall prevalence of ASDs ranged from 4.5 to 9.9 per 1,000 children, with an average prevalence of 6.7 per 1,000 children. The highest prevalence was observed in New Jersey (9.9 per 1,000), while West Virginia had the lowest (4.5 per 1,000). The male-to-female ratio varied from 2.8:1 to 5.5:1. Most children with ASDs received special education services, and the median age of the first documented ASD diagnosis was around 52-56 months. The report highlights the importance of early identification and intervention for children with ASDs and suggests that ongoing surveillance and studies are necessary to better understand the prevalence and characteristics of ASDs in the United States.The report presents the findings of the Autism and Developmental Disabilities Monitoring (ADDM) Network, a population-based surveillance program, which aimed to determine the prevalence of autism spectrum disorders (ASDs) in children aged 8 years across six sites in the United States in 2000. The study used a multi-source, records-based approach to collect data from educational and health sources, with clinician review to confirm cases. The overall prevalence of ASDs ranged from 4.5 to 9.9 per 1,000 children, with an average prevalence of 6.7 per 1,000 children. The highest prevalence was observed in New Jersey (9.9 per 1,000), while West Virginia had the lowest (4.5 per 1,000). The male-to-female ratio varied from 2.8:1 to 5.5:1. Most children with ASDs received special education services, and the median age of the first documented ASD diagnosis was around 52-56 months. The report highlights the importance of early identification and intervention for children with ASDs and suggests that ongoing surveillance and studies are necessary to better understand the prevalence and characteristics of ASDs in the United States.