The more recent literature addressing the clinical phenomenology of presenile dementia is reviewed. This survey, spanning approximately the past 4 decades and comprising a large number of articles in scientific journals, reveals that reported epidemiological data, symptoms and signs, and results of ancillary tests often vary widely from study to study, especially as regards findings of history and of mental status and neurological examinations. There is considerable indication that diagnostic specificity in presenile dementia in the absence of pathological examination of the brain by tissue biopsy or at autopsy may not be as reliable as is generally thought to be the case. The observed problems with interstudy agreement are discussed and are seen to be due in large measure to methodological inconsistency and nonuniformity. Areas of difficulties in methods are identified and guidelines for subsequent, needed clinical studies are suggested.