We studied the prevalence of dementing disorders in a rural town of Japan (Amino-cho), using a door-to-door two-phase design. Of the 170 persons screened as having cognitive impairment, 142 cases were diagnosed as having dementia. The prevalence (cases/100 aged 65 years older) was 3.8 for all types of dementia, 2.1 for Alzheimer's disease (AD), 1.0 for vascular dementia (VD) and 0.7 for other types of dementia. Among other types of dementia, there were four male patients with dementia with Lewy bodies (prevalence: 0.1), but no patients with frontotemporal lobar degeneration. The overall prevalence was higher in women for AD, while that of VD was the same in both sexes. With results similar to many previous studies in Western countries and some recent surveys in Japan, the present sudy clearly showed that AD is more prevalent than VD.