In this program of research we propose to study genetic factors, brain- behavior relationships, and aspects of developmental course in autism and related conditions. The concern with basic mechanisms and clinical disorders gives rise to the interdisciplinary and transdisciplinary nature of the research. Goals of this program of research include: 1) localization of genes in autism through a systematic genome search and candidate gene analysis, 2) better definition of the broad phenotype of autism by examination of neuropsychological, social, cognitive, and psychiatric profiles of first degree relative of patients with autism and Asperger's syndrome and to determine whether homogeneous subtypes of autism are transmitted within families, 3) to clarify the neuroanatomic correlates of autism through neuroimaging, and 4) to examine issues of the stability of the phenotypes of autism and related conditions (including Childhood Disintegrative Disorder) through systematic follow-up studies. Four projects and three core resources are proposed. Projects include: 1) Molecular genetics of autism and related conditions, 2) family genetics, 3) neuroimaging, and 4) longitudinal studies. The longitudinal follow-up project has and explicit clinical focus. Three core resources are proposed: 1) administration, 2) diagnosis and assessment, and 3) data management and statistics. The Program Projects builds on a network of existing collaborations and makes use of important clinical resources at each site.