In a cooperative study coordinated by WHO, stroke was registered between 1971 and 1974 in 17 centres both in developing and developed countries. A common operating protocol was used to obtain comparable data. Age-adjusted incidence of stroke shows moderate geographical variations, cerebrovascular accidents being common in all the contrasting populations studied in various parts of the world. Data were also obtained on the types of management of stroke patients, their survival rates, and functional prognosis. Control of hypertension, although known to be effective in the prevention of stroke, seemed to be insufficient in most countries. It is concluded that stroke registers may be used as a source of information for the planning and implementation of stroke control programmes in the community.