<p>Adults with schizophrenia exhibit substantial and widespread cognitive impairment, with subtle cognitive deficits already apparent in childhood and adolescence - many years prior to the onset of psychosis. Here, we focus on evidence from population-based research highlighting findings specific to cognitive impairment (as indexed by IQ) that precedes the onset of schizophrenia. We illustrate that (i) cognitive impairment worsens from early childhood onwards through to the onset of psychosis; (ii) this early and progressive cognitive impairment is rarely present in other psychotic disorders. At the same time, (iii) early cognitive impairment is not universal in schizophrenia; and (iv) a substantial role for genes affecting both schizophrenia and early life cognitive impairment has not been unequivocally proven. We suggest that a subgroup of patients with schizophrenia is characterized by progressive premorbid cognitive impairment. This group is developmentally distinguishable from the rest of patients with psychoses. Future studies should focus on understanding the (possibly unique) etiology in this neurodevelopmental subgroup of schizophrenia patients.</p>