A number of lines of evidence converge in implicating neurodevelopmental processes in theetiology and epigenesis of schizophrenia. In this study we used a prospective, longitudinal designto examine whether adverse obstetric experiences predict schizophrenia and whether there is adeviant functional–developmental trajectory during the first 7 years of life amongindividuals who manifest schizophrenia as adults. The 9,236 members of the Philadelphia cohortof the National Collaborative Perinatal Project were screened for mental health service utilizationin adulthood, and chart reviews were performed to establish diagnoses according to DSM-IVcriteria. The risk for schizophrenia increased linearly with the number of hypoxia-associatedobstetric complications but was unrelated to maternal infection during pregnancy or fetal growthretardation. Preschizophrenic cases (and their unaffected siblings who were also cohortmembers) manifested cognitive impairment, abnormal involuntary movements and coordinationdeficits, and poor social adjustment during childhood. There was no evidence of intraindividualdecline in any domain, but preschizophrenic cases did show deviance on an increasing number offunctional indicators with age. Together, these findings suggest that both genetic and obstetricfactors participate in creating a neural diathesis to schizophrenia, the phenotypic expressions ofwhich are age dependent, probably reflecting the maturational status of a number ofinterconnected brain systems.