An epidemiological survey of primary dementia syndromes was conducted in the city of Bra (26287 residents) in the Piedmont region. All the patients for whom a diagnosis of senile dementia had already been recorded together with the cases coming to light as a result of a questionary circulated to general practitioners and neuropsychiatrists were subjected to a broad battery of neuropsychological tests. The prevalence rate proved to be 255 (+/- 61) per 100 000 of the population and 2028 (+/- 476) per 100 000 of the over 65s. Close attention was paid to dements living in nursing facilities. Factors favoring institutionalisation were: advanced age, severe motor impairment and female sex. No correlation between severity or dementia and institutionalisation was found.