The pervasive developmental disorders (PDD), as exemplified by infantile autism, are a group of severe childhood neuropsychiatric disorders of early onset in which multiple areas of social, communicative, and cognitive development are disturbed. Although these disorders often are associated with some degree of mental retardation and various medical and neurological abnormalities, they are distinctive in their course and outcome, and in the patterns of development deficit. These conditions, which are expressed as the final behavioral syndrome, probably have many different causes. Whereas organic factors clearly are implicated, no precise etiological mechanisms have been established. Management of these disorders includes appropriate educational and behavioral intervention. Efforts are needed to define these disorders more precisely, and to identify relevant subgroups, to further studies of pathophysiology.