The EEG in normal aging and in dementia due to a variety of diseases has been described. In dementia due to degenerative diseases, metabolic disorders, normal pressure hydrocephalus, and deficiency states, the diffuseness of the abnormalities observed has been emphasized; whereas with cerebrovascular disease and with intracranial massess, the focal nature of the changes has been stressed. Although a normal EEG does not rule out the diagnosis of dementia especially in its early stages, the EECG can nevertheless be a significant instrument in the identification or organic processes when the diagnosis is uncertain, in differentiating diffuse from focal cerebral lesions, and in following the course of the disease. Because electroencephalography is easily performed, is safe, and can be frequently repeated, it should be considered one of the more useful tools in the clinical evaluation of patients with dementia.