OBJECTIVE: Neurological abnormalities found in schizophrenic subjects and their healthy relatives have raised questions concerning etiology. The aim of the present study was to investigate the genetic and environmental antecedents of neurological impairment in monozygotic twins discordant for schizophrenia, with particular focus on the well discordant twins. The etiological factors of interest were history of obstetric complications, family history of psychosis, history of substance abuse, and history of postnatal cerebral trauma. METHOD: History of obstetric complications, including information from pregnancy through the neonatal period, and data on neurological "hard" and "soft" signs were obtained blindly and separately for each member of 22 monozygotic twin pairs discordant for schizophrenia and seven normal comparison monozygotic twin pairs. Clinical and family interviews provided information about background factors. RESULTS: Degree of neurological impairment in the well discordant monozygotic twins was significantly positively related to history of both neonatal and total obstetric complications. None of the three other background factors investigated was related to degree of neurological impairment in the ill or well co-twins. CONCLUSIONS: The contribution of obstetric complications to the current level of neurological impairment in well discordant co-twins suggests that the spectrum of neuroabnormality, ranging from neurological signs to schizophrenia, in monozygotic discordant twins may be the result of subtle gene-environment interaction.Abstract Teaser