The geography of dementia: an approach through epidemiology.

Dementia is an extremely common condition among the elderly. Over 100 epidemiological surveys have now been published from many countries. Methodological differences make comparisons difficult, although meta-studies carried out in Europe provide baseline material for developed countries. Surveys within each geographical area which has been studied are discussed. Differences in the distribution of sub-types of dementia and the resultant challenges to governments and researchers are set out.