Autism is a lifelong neurodevelopmental disorder characterized by early onset of impairments in social interaction and communication and unusual, stereotyped behaviors. Autism (i.e., autistic disorder) often is classified with two related, although less severe, developmental disorders: Asperger disorder and pervasive developmental disorder--not otherwise specified. These three constitute the autism spectrum disorders (ASDs). Diagnosis of ASDs is based exclusively on developmental pattern and behavioral observation. Two population-based studies conducted by CDC in selected U.S. locations reported ASD prevalence of 3.4 and 6.7 per 1,000 children, respectively. CDC also conducts two nationally representative surveys, the National Health Interview Survey (NHIS) and the National Survey of Children's Health (NSCH), in which parents are asked whether their child ever received a diagnosis of autism. Because of similarities in methodology used by the two surveys, CDC analyzed 2003-2004 data from NHIS and data from the first-ever NSCH (collected during January 2003-July 2004) to 1) estimate the population-based prevalence of parental report of diagnosed autism in the United States and 2) assess parental reporting of child social, emotional, and behavioral strengths and difficulties and special-health care needs among children with and without reported autism. This report describes the results of that analysis, which indicated that the prevalence of parent-reported diagnosis of autism was 5.7 per 1,000 children in NHIS and 5.5 per 1,000 children in NSCH. Prevalence estimates in the two studies were similar across age, sex, and racial/ethnic populations. The consistency in estimates between the two surveys suggests high reliability for parental report of autism. These estimates suggest that, as of 2003-2004, autism had been diagnosed in at least 300,000 U.S. children aged 4-17 years. In addition, parental reports of autism were associated with reported social, emotional, and behavioral symptoms and specialized needs. Thus, these surveys might be useful to assess health, education, and social service needs of children with autism.