Dementia — that is, irreversible and usually progressive destruction of the brain in old age, the causes of which have yet to be identified – is arguably the most significant single problem currently facing the health services. Ten per cent of the population aged 65 years and over (more than 700,000 people) are affected by the condition (s) and of these about half exhibit symptoms of a severe degree. The characteristic clinical features are usually associated with a loss of and structural changes in certain brain cells and include failing memory, intellectual deterioration and behavioural disturbance. The speed and extent of this disintegration of personality vary considerably but for the more severely affected the outcome is almost invariably a shortened life expectancy and a steadily diminishing capacity to undertake simple everyday tasks culminating eventually in an inability to survive without considerable assistance.

This paper describes the nature of the condition(s), the pattern of occurrence and the current and projected problems in the provision of health and social services for the elderly demented. It also attempts an assessment of the economic and social implications of dementia in old age. Finally, it examines the present state of knowledge about the causes of dementia and the barriers’ to further scientific advance both in this area and in the development of effective medical intervention.