Dementia is an important public health problem as it is one of the most common diseases in the elderly and a major cause of disability and mortality. This review on dementia is restricted to European Union countries where the overwhelming majority of studies have been undertaken, and will also refer to the EURODEM publications which may be considered to be the principal European reference point in this area. In subjects aged over 65, crude prevalence rates for dementia varied between 5.9% and 9.4%. We discuss the major problems limiting the use of these estimations, limits which may differ according to the area of application, be it etiological research or care provision.