The prevalence of dementia was studied in 887 males and females Hisayama residents aged 65 or over (screening rate, 94.6%) using clinical information, neurological examination and dementia scales. We found 59 cases with dementia, the prevalence being in 6.7% of the screened population with females predominant. Vascular dementia was more frequent, with the ratio of vascular dementia to senile dementia of Alzheimer's type being 4.5 for males and 1.2 for females. Brain-pathology in 47 cases with dementia out of 59 was examined by CT scan or at autopsy during the subsequent 20-month period. Based on the morphologic diagnoses, vascular dementia was high in frequency at 55% of the demented cases, being three times higher than senile dementia of Alzheimer's type.