The prevalence of Autism and other Autism Spectrum Disorders (ASDs) has increased dramatically in recent years. The criterion for a clinical diagnosis of Autism, however, is independent from the special education eligibility requirements for Autism services. While the DSM-IV-TR provides a nationally-accepted definition for Autism and ASD, under federal law, the special education criteria for Autism services can vary from state to state. By analyzing federal, special education child-count data as well as each state's legal code, this study examines and compares eligibility criteria in all 50 states and Washington DC. Our results reveal inter-state variability in Autism eligibility requirements within special education, and this variability can have an impact on prevalence rates. Implications and recommendations for researchers and practitioners in clinical psychology, public health, education, pediatrics, and public policy are discussed.