ABSTRACT.In elderly individuals suspected to have dementia, EEG changes are different from those in normal aging. In the early stages of dementia due to degenerative disorders of the CNS (e.g. Alzheimer's disease), the EEG is either normal or shows scattered theta-delta activities and decreasing frequency of the alpha rhythm. As the disease progresses, the EEG is almost always abnormal and the severity of the slowing is increased. In toxic-metabolic causes of intellectual impairment, the EEG abnormalities are more pronounced and include continuous medium-to-high amplitude anterior dominant theta-delta activities. In patients with dementia due to focal CNS insult (e.g. multiple infarcts, neoplasm, etc.), the EEG may show focal slowing and/or suppression of the background rhythms on the involved site. In certain dementing processes, EEG features may be more specific although not pathognomonic; e.g. periodic sharp waves in Jakob-Creutzfeldt disease, low amplitude background activities in Huntington's disease, paroxysms of sharp and spike waves superimposed on a slow background in dialysis dementia. EEG is most helpful in separating organic dementia from pseudodementia. Normal EEG or age-related changes support the later diagnosis. Since EEG is easily available and noninvasive, it is one of the most important screening tests in patients suspected of dementia.