The relationships between post-mortem findings and electroencephalographic tests obtained during the 12 mo before death were investigated for 100 psychogeriatric subjects. The results, which due to methodological limitations are only tentative, suggest a fairly close correlation between the two sets of data, which can, however, be obscured by a number of factors, notably the presence of severe physical illness (cerebral and systemic, including severe drug effects) of a nonstructural type at the time of the EEG. In their absence, diffuse EEG slowing strongly suggests senile-Alzheimer's brain disease (it is associated with plaque and tangle formation, ventricular dilatation, and cortical atrophy); and intermittent lateralized slow waves strongly suggest hemodynamic problems due to sclerosis of cerebral arteries. Brain lesions produce EEG changes mostly if large and close to the cortex. If the necessary precuations in EEG interpretation are taken (i.e., mainly consideration of present clinical state), the EEG is diagnostically quite helpful in this group of subjects.