Neuropsychological deficits in schizophrenia and affective illnesses have been a topic of increasing research interest for more than two decades. Currently, the cognitive dysfunctions are regarded as an essential element of these illnesses, Occurring already in their prodromal phase, with an increment during the Course of illness and with some deficits persisting also during the remission period. In schizophrenia, deficits in working memory and executive functions are most frequently demonstrated. In patients with affective illnesses, the initial research focused mainly on depression, where psychomotor slowness, deficits of attention, verbal and working memory and executive functions have been observed. It has been shown that during depression in the course of bipolar affective illness, the cognitive dysfunctions have been more marked as compared with recurrent depression. In this paper, the neuropsychological changes occurring during the period of mania and hypomania have been presented. The disturbances that have been shown most frequently include selective cognitive dysfunctions such as disturbances of attention and learning process, working memory and executive functions. During periods of mania/hypomania, the specific distortions of thinking occur (anastrophic thinking), as well as disturbances in the decision making process, connected with increased impulsivity. Another characteristic of the episode of elevated mood has been a change of information processing of affective type, mostly a lower ability for perception and recognition of negative emotions. Among persons with bipolar affective illness, especially during the hypomanic period, an increased level of creativity than in control persons has been observed, what may facilitate higher artistic activity. Recently, the evidence has been accumulated pointing to more severe cognitive dysfunctions in bipolar affective illness, type I (with manic states) compared with bipolar affective illness, type 11 (with hypomania).