Positron emission tomography (PET) is a valuable tool for understanding of functional correlates of biological and structural changes in brain of patients with various dementia diseases. As such it can provide valuable physiological correlates important for diagnosis, management and research of dementia disorders. A crucial question is whether PET is capable of early or preclinical detection of dementia. Longitudinal PET studies in Alzheimer families with chromosomal aberrations will be important for. Impairment of cerebral blood flow and glucose metabolism is a common feature in patients with Alzheimer's disease. The pattern of changes is distinct from other forms of dementia and correlates with neuropsychological impairments. Neuroreceptor studies have to be further applied as well as monitoring of drug treatment effects.