Dementia disorders are today considered to be a major driver of costs in health care and social systems and worrying estimates of future dementia prevalence have been presented. It is of great interest for policy makers to have an estimate of dementia disorders' contribution to global social and health care costs, particularly in light of the demographic prognoses. The worldwide costs of dementia were estimated from prevalence figures for different regions, and cost-of-illness studies from key countries using a model based on the relationship between direct costs of care per demented and the gross domestic product per capita in each country. The worldwide direct costs for dementia in 2003 are estimated at 156 billion USD in the main scenario based on a worldwide prevalence of 27.7 million demented persons (sensitivity analysis: 129-159 billion USD). Ninety-two percent of the costs are found in the advanced economies with 38% of the prevalence. Although there are several sources of uncertainty, it is obvious that the worldwide costs are substantial and the expected increase in elderly people in the developing countries presents a great challenge.