A group of 40 patients (22 male and 18 female) with bipolar affective disorder were examined with lateralization tests from the Halstead-Reitan Neuropsychological Test Battery and their performance was related to brain image obtained by means of MRI. The number of left-handers was somewhat lower than that in the general population. In the group of patients with bipolar affective disorder functional cerebral asymmetry was found to be different in men than that in women. In remission period no evidence was obtained indicating differences in hemispheric asymmetry of function between the group under study and the general population. No relationship was found between the size of particular cerebral structures measured by means of MRI and the hemispheric asymmetry of function. The study has confirmed the role of the corpus callosum for interhemispheric transfer, as well as the relationship between temporal lobes and cognitive functions in bipolar affective disorder.