It has become increasingly apparent that schizophrenic patients can suffer from many cognitive deficits (Hemsley, 1982). These include a decline in IQ (Nelson et al, 1990), loss of concentration (Garmezy, 1978), and various ‘executive’ difficulties similar to those observed in patients with frontal lobe lesions (Morice, 1990). The availability of a large, population-based sample of schizophrenic patients in the Harrow study provided the opportunity to examine the prevalence of these impairments and to relate them to the signs and symptoms of the disorder.