BACKGROUND: Recent neurodevelopmental models of schizophrenia, together with substantial evidence of neurocognitive dysfunction among people with schizophrenia, have led to a widespread view that general cognitive deficits are a central aspect of schizophrenic pathology. However, the temporal relationships between intellectual functioning and schizophrenia-spectrum illness remain unclear.MethodLongitudinal data from the Copenhagen High-Risk Project (CHRP) were used to evaluate the importance of intellectual functioning in the prediction of diagnostic and functional outcomes associated with the schizophrenia spectrum. The effect of spectrum illness on intellectual and educational performance was also evaluated. The sample consisted of 311 Danish participants: 99 at low risk, 155 at high risk, and 57 at super-high risk for schizophrenia. Participants were given intellectual [Weschler's Intelligence Scale for Children (WISC)/Weschler's Adult Intelligence Scale (WAIS)] assessments at mean ages of 15 and 24 years, and diagnostic and functional assessments at mean ages 24 and 42 years. RESULTS: Intellectual functioning was found to have no predictive relationship to later psychosis or spectrum personality, and minimal to no direct relationship to later measures of work/independent living, psychiatric treatment, and overall severity. No decline in intellectual functioning was associated with either psychosis or spectrum personality. CONCLUSIONS: These largely negative findings are discussed in the light of strong predictive relationships existing between genetic risk, diagnosis and functional outcomes. The pattern of predictive relationships suggests that overall cognitive functioning may play less of a role in schizophrenia-spectrum pathology than is widely believed, at least among populations with an evident family history of schizophrenia.