The borderline condition between normal aging and dementia is a major issue of concern for health policy planning because of an early intervention for possible prevention of dementia. Since 1988, the author has been involved in a community-based program on stroke, dementia, and bed-confinement prevention in Tajiri, northern Japan (the Osaki-Tajiri Project). As a part of the project, a cross-sectional study of aged patients with mild cognitive impairment in Tajiri was undertaken to investigate the clinical features of the condition, in addition to a longitudinal study to research its progression to dementia with possible risk factors. Impairment of the basic functions of attention and executive function was noted, as opposed to impairment in the cognitive domain itself. Magnetic resonance imaging (MRI) findings showed a pattern close to that of healthy persons in their 80s, rather than that of patients with cognitive deficit. The results of the longitudinal study showed more progression to dementia when the Clinical Dementia Rating (CDR) was 0.5 in domains other than memory. No effects of lifestyle, internal diseases or psychosocial intervention were confirmed. In progression to Alzheimer's disease, generally low cognitive function and general atrophy were involved, whereas frontal lobe function, atrophy of the frontal and temporal lobes, white matter changes and cerebral infarction were related to progression to vascular dementia. For health policy planning for dementia prevention, we consider that excessive dependence on primary prevention should be avoided; rather, secondary prevention, using the CDR, psychological testing and MRI are desirable.