Dementia is an acquired disorder of higher cerebral functions and cognition. Because of increasing life expectancy dementia poses a major health and socio- ecomic problem. Alzheimer's disease accounts for 70-90% of mental decline in the elderly. Degenerative n-Alzheimer's dementi as are responsi- ble for 7-30%. These include a variety of disorders clinically characterised by progressive cognitive dysfunction often combined with focal neurological def- icits, e.g. Parkinson-plus syndromes, Lewy body dementia, lobar and multisys- tem atrophies, other neurodegenerative disorders, and prion diseases. Often it is difficult to distinguish these illnesses from Alzheimer's disease and vascu- lar dementia. In spite of considerable progress in molecular genetics, biochemistry, and neuropathology, the classification and pathogenesis of n-Alzheimer's dementias are still debatable. Diagsis is frequently made only at postmor- tem. Because disease markers are t available for the majority of n- Alzheimer's dementias, consensus criteria for the identification of such diseas- es are warranted. These criteria could serve at a basis for early diagsis and distinction from other dementing disorders.