We assessed premorbid functioning during childhood and adolescence in 50 people with schizophrenia from multiply affected families, 39 of their unaffected siblings, 69 people with schizophrenia with no family history of psychosis, 67 of their unaffected siblings and 83 controls. People with schizophrenia had poorer premorbid social and academic adjustment and exhibited a decline between childhood and adolescence compared with controls. Unaffected siblings from multiply affected families also had poor academic functioning in adolescence, with a decline between childhood and adolescence.This may represent a familial (presumed genetic) effect. Declaration of interest: None. E.B. and CM. supported by the Wellcome Trust.