IMPORTANCE Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder. Previous surveys have reported a steady increase in ASD prevalence in US children over the past decades. Several behavioral therapies and medications have been developed to treat the symptoms of ASD; however, little is known about the current status of treatment usage for children diagnosed as having ASD. OBJECTIVE To estimate the prevalence and treatment patterns of ASD among US children using nationally representative data. DESIGN, SETTING, AND PARTICIPANTS This study used data from the 2016 National Survey of Children's Health, a nationwide, population-based, cross-sectional survey. We included 43 032 children aged 3 to 17 years. Data were collected through questionnaires completed by a parent or guardian. Data were analyzed from February 2018 to March 2018. MAIN OUTCOMES AND MEASURES Outcome variables included ASD diagnosed by a physician or health professional and the use of behavioral treatment or medication treatment among children with ASD. RESULTS Of the 43 032 included participants, 22 072 (51.3%) were male, and the mean (SD) age was 10.7 (4.4) years. The weighted prevalence of ever-diagnosed ASD and current ASD were 2.79% (95% CI, 2.46-3.12) and 2.50% (95% CI, 2.21-2.79), respectively. The state-level prevalence of ever-diagnosed ASD varied from 1.54% (95% CI, 0.60-2.48) in Texas to 4.88% (95% CI, 2.72-7.05) in Florida. Nationally, about 70% of children with current ASD (70.5%; 95% CI, 65.1-75.8) were treated; 43.3% (95% CI, 37.4-49.2) received behavioral treatment only, 6.9% (95% CI, 3.7-10.1) received medication treatment only, and 20.3% (95% CI, 16.5-24.1) received both behavioral and medication treatments. The remaining 29.5% (95% CI, 24.2-34.9) of children with current ASD did not receive either behavioral or medication treatment. CONCLUSIONS AND RELEVANCE This study showed that the prevalence of ASD in the United States was relatively high, and it varied substantially across US states. Almost 30% of US children with ASD did not receive behavioral or medication treatment, which calls for a critical need to understand and address the barriers for those children to receive appropriate treatments.