Research has suggested that poor insight in patients with schizophrenia is associated with poorer treatment compliance and outcome. Little is known about the etiology of poor insight. Poor insight has been attributed to a willful preference for illness, a psychological defense, and cognitive impairments. To test the hypothesis that poor insight is related to enduring cognitive deficits, the performance of 29 patients with schizophrenia and impaired insight and 63 patients with schizophrenia and unimpaired insight was compared on repeated administrations of the Wisconsin Card Sorting Test. Results indicate that subjects with impaired insight demonstrate consistently poorer performance over a period of 1 year than subjects with unimpaired insight. When the effects of IQ were partialled out, subjects with impaired insight made significantly more perseverative errors and achieved fewer categories correct, a pattern of performance deficits identified with neuropsychological dysfunction in schizophrenia. These results support the hypothesis that cognitive impairment may underlie poor insight in schizophrenia.