In France the prevalence of pre-lingual deafness is between 1 and 1.4 per 1000 habitants, and according to very conservative estimates, about 44 000 deaf persons use the sign language. Additionally, the prevalence of dementia in France is close to 1% (850 000 dements for a total population of 65 millions). The prevalence of dementia in pre-lingual deaf adults has also been described and is between 1 and 1.4 /100 000 habitants.