Ventricular enlargement is one of the most consistently documented neurobiological abnormalities in schizophrenia. The timing of the development of this abnormality in the course of schizophrenic illness and its relationship to neuropsychological dysfunction and premorbid adjustment is, however, unclear. To address these questions, we examined the relationship between ventricle-brain ration (VBR), premorbid adjustment, and neuropsychological function, in 23 acutely exacerbated chronic schizophrenic inpatients. We obserged that larger ventricles were associated with better current neuropsychological test performance, better premorbid cognitive ability, greater cognitive deterioration, better childhood premorbid social function, and greater decline in social function from premorbid levels. These data suggest that at least two developmental processes may operate in the genesis of cognitive and social dysfunction in schizophrenia: (1) childhood onset associated with poor premorbid childhood function, low educational achievement, lower intelligence quotient (IQ) and variably with VBR; and (2) adolescent onset associated with relatively normal childhood social function, higher academic achievement and IQ and increased VBR. Ventricular enlargement may reflect a late developmental or degenerative pathological process in schizophrenia. © 1994.