The objective of the study is to estimate the prevalence of dementia u
sing the data of the Paquid cohort. A sample of 3 149 subjects aged 65
years and older living at home or in institution was randomly chosen
in Gironde (France). A questionnaire and psychometric tests were used
to evaluate cognitive functioning and the presence of dementia was ass
essed through DSM III Diagnostic and Statistical Manual of mental diso
rders (ed. III) criteria. Hachinski scale and work group NINCDS-ADRDA
criteria were applied to confirm the presence of dementia and identify
Alzheimer's disease. Overall prevalence was estimated to 4.3 %. No di
fference was found between men and women. The prevalence increased wit
h age with nearly a doubling every 5 years of age. In institution, dem
entia frequency remained stable. The relative risk of a demented subje
ct to be institutionalized with regard to a non demented subject decre
ased with age.