Abstract: Alzheimer disease(AD) is the most common type of dementia and will become increasingly prevalent with population aging. It is accepted that the pathologic changes underlying AD appear in the brain years to decades before the symptomatic stages. Clinical measures of cognitive impairment, as used for definition of dementia, will not allow early diagnosis of AD-pathology in the mild or asymptomatic stages. There has been growing interest in early diagnosis of this disease, particularly regarding the initiation of new treatment strategies ahead of the onset of irreversible neuronal damage. Brain imaging markers are among the most promising candidates for this diagnostic challenge. PET has been demonstrated to be a most sensitive, specific, noninvasive, objective and quantitative method for early identification of AD-pathology and molecular biology, thus for prediction of dementia of the Alzheimer type, even in the mild and asymptomatic stages.