We analysed the structure of the brain bioelectric activity in patients with the initial stages of atherosclerotic, hypertonic and mixed discirculatory encephalopathy (DE) (n=140) of middle age (51.44±5.9 years), as well as participants from the control group (n=51) of the appropriate age. At the initial stage of hypertensive DE, changes in the power of individual rhythms of brain bioelectric activity are more pronounced than in the initial stage of atherosclerotic DE. In particular, at the initial stage of hypertensive DE, the power in the range of slow rhythms (delta- and theta-rhythm) in the frontal regions of both hemispheres, as well as in the temporal, occipital and central region of the right hemisphere, is significantly higher. There were no significant intergroup differences of the alpha and beta rhythms power. Thus, on the initial stage of hypertensive DE, the dysfunction of subcortical structures that are generating delta- and theta-rhythms is more pronounced than in the initial stage of atherosclerotic DE.