The research proposed is a three year cross-sequential study of the cognitive and motor skills and social and affective behaviors of 120 children with pervasive developmental disroders (PDD), who have been diagnosed by a child psychiatrist as meeting the DSM-III diagnostic criteria for either infantile autism (IA) or childhood onset pervasive developmental disorder (COPDD). Children diagnosed as having IA or COPDD will be recruited into six age groups of 20 children each. At the time of initial testing the sample will consist of 20 4 year olds, 20 6 year olds, 20 8 year olds, 20 10 year olds, 20 12 year olds, 20 14 years old. Each of the children in the PDD sample will have two normal control matches--a verbal mental age match, and a non-verbal mental age match. Children in the PDD sample will be tested once a year for three years on a neuropsychological test battery: normal controls will be tested once, in year two of the study. In years one and three, children in the PDD group will be videotaped in 2 20 minute structured sessions, and parents and teachers will be asked to complete a behavior checklist. The long-term objectives of this study are fourfold: to determine the pattern of development of cognitive skills in IA and COPDD diagnosed children; to separate normal-but-delayed from deviant aspects of language development in the PDD sample; to construct, through empirical methods, cognitive skill profiles and behavioral profiles for the PDD children; and to explore the relationship between cognitive skill profiles and behavioral profiles and to examine their joint relationship with the DSM-III diagnoses of IA and COPDD. The six specific aims of the study are : (1) to determine whether a previous finding of a post-pubertal decline in cognitive skills is replicated in this sample; (2) to construct and cross-validate cognitive profiles; (3) to analyze the stability of cognitive profiles cross-sequentially; 4) to construct and validate behavioral profiles; (5) to determine joint distributions of cognitive and behavioral profiles and DSM-III diagnostic categories; and (6) to combine present data with previously collected data on the language development of 177 children with PDD in order to generate a large-scale contrastive developmental profile of linguistic skills. It is hoped that the empirical construction of valid subgroups, and clearer understanding of cognitive development will help to better define classification criteria, and aid study of biological markers.