Patients with schizophrenia exhibit an exceedingly wide range of symptoms from a variety of domains. The cardinal features are abnormal ideas (such as delusions); abnormal perceptions (such as hallucinations); formal thought disorder (as evidenced by disorganized speech); motor, volitional, and behavioral disorders; and emotional disorders (such as affective flattening or inappropriateness). In addition to these diverse, and sometimes bizarre symptoms, it has become increasingly apparent that the disorder is, to variable degrees, accompanied by a broad spectrum of cognitive impairments. This review addresses the question of whether the cognitive deficits seen in schizophrenic patients are the core features of the disorder. In other words, we explore whether schizophrenia is best characterized by symptoms or cognitive deficits (we suggest the latter) and moreover, whether there is a specific cognitive deficit profile that may assist in diagnosis. First, we discuss what the cognitive deficits are. Then we address in turn the reality, frequency, predictive validity, specificity, course and susceptibility to neuroleptic effects of these cognitive impairments. In brief, we argue that various cognitive deficits are enduring features of the schizophrenia illness, that they are not state-related and are not specific to subtypes of the illness, and, more specifically, that working memory and attention are characteristically impaired in patients with schizophrenia, irrespective of their level of intelligence. Last, we conclude that problems in these cognitive domains are at the very core of the dysfunction in this disease.