Criteria for the diagnosis of clinically significant (pervasive) dementia in the community elderly are described. Satisfactory reliability was achieved by both psychiatrists and nonpsychiatrists in applying these criteria to systematic descriptions of psychopathology in a random sample of elderly subjects living in the community. The validity of the concept of pervasive dementia is established by reference to associated disability and mortality rates. The utility in geriatric epidemiology of the diagnosis of pervasive dementia is compared with that of face-to-face diagnosis based on the International Classification of Disease (9th Edition).