We report positron emission tomography (PET) findings of our patients with vascular dementia, asymptomatic cerebral infarction, and chronic cerebral circulatory insufficiency. According to the PET studies, it was suggested that frontal lobe hypoperfusion and hypometabolism play important roles in dementia caused by cerebral infarctions. It was also suggested that patients with subjective complaints associated with asymptomatic strokes and patients with chronic cerebral circulatory insufficiency already exhibited decreased cerebral circulation. Since therapeutic approaches to vascular dementia after its development are limited, active control of risk factors and prevention of recurrent stroke during the developmental process of vascular dementia are important. We review recent situations in prevention and treatment of vascular dementia.