Psychometric tests which assess cognitive brain function in dementia disorders are partly prone to artifacts, e.g., the experience of the investigator and the cooperation of the patient influences the results. An objective way to assess the degree of cognitive disturbance could be to measure neuronal activity represented by the electrical brain activity. The aim of the present study was to investigate how well cognitive function in dementia assessed by psychometric tests correlates with electrical brain activity (EEG). Multichannel EEG data was reduced into 3-D intracerebral equivalent dipole EEG generators allowing a more convenient statistical data management and valid physiological data interpretation. 35 patients suffering from dementia of Alzheimer type were investigated. An increase of dipole strength in the slow frequency bands, a more anterior equivalent dipole of alpha- and beta-activity, and a slowing of the EEG with increasing cognitive deterioration could be demonstrated. The results support the hypothesis that the amount of disturbance of cognitive function in dementia can be assessed by measuring the electrical activity of the brain.