Many children with autism have problems with sleep, learning, mood, and behavior, as well as developmental and neuropsychological issues. The present study will attempt to address the relationships between these issues, and estimate the frequency and types of these problems in the autistic population. Researchers will analyze two large existing datasets: a general population sample of 500 children from a National Institutes of Health-funded sleep study, and a clinically diagnosed sample of 1250 children evaluated in a psychiatry diagnostic clinic, including 250 children with autism. Each of these samples includes detailed data collected on sleep problems, neuropsychological measures of attention, memory, language and reasoning, IQ scores, reading and math achievement test scores, parent rating scores assessing behavior, and developmental and medical histories of the children participating. Using statistical methods, this study will try to untangle the relationships between these measures, to determine which are associated with each other, and which are specific to various forms of autism (low-functioning versus high-functioning). This large-scale analysis should help to inform clinicians, educators, and medical practitioners about the frequency and types of problems in autism. Understanding the relationships between these problems may also help to guide intervention programs, and identify subgroups of children with autism who are at risk for particular problems.