The proposed research is designed to assess the hypothesis of a core/primal executive function deficit in autism. The proposed study will examine the hypothesis that executive function deficits are present early in the lives of autistic children and may therefore underlie other later appearing symptoms of autism. This hypothesis will be tested in autistic preschool children (mean age = 4 years n=20). These children are younger than those in whom executive function deficits have been previously discovered. The autistic children's performance will be compared to mental age and chronological age matched developmentally delayed controls, as well as to normally developing chronological age matched controls. Executive function abilities will be assessed with a series of eight age-appropriate tasks which have been linked to frontal functioning by previous research. The subjects in this study are also being assessed on their joint attention, social interaction behavior regulation, and imitation abilities. and the relation between executive functions and these skills will be examined. Finding executive function deficits at an early age in autism would provide support for a theory of a primary executive function deficit in autism: however, not finding deficits in these children would reject this prominent hypothesis of the core cognitive deficit in autism. Either result also has implications for understanding the social and emotional characteristics of autistic individuals, as well as for diagnostic and treatment programs.