Hypertension is a major health problem and contrary to ischemic heart disease, which occurs only in Western countries, its distribution is almost universal. It is this universality that has prompted us to gather, in this book, data on arterial blood pressure obtained in different parts of the world. Moreover, cerebrovascular mortality, which is the commonest cause of death from hypertension, is decreasing in most Western countries and in Japan, and the reasons for this are still far from clear. A major problem in comparing blood pressure values from different centers is the standardization of the measurement. Complete standardization will never be achieved if one takes into account the numerous factors that may influence blood pressure in epidemiological studies. Whether blood pressures are measured by doctors or by technicians, are recorded at home, in the working place or in a hospital, in sitting, standing or supine position, and is taken during the same examination-all of these whether a blood sample factors can influence blood pressure measurement. But meals, time of day (blood pressure being higher in the evening), heart rate, cuff size, stethoscope used, digit preference, month of year, temperature, etc., can equally influence the measurement. Home reading of arterial blood pressure at standardized times is probably the best answer to all of these problems and has been used with gratifying results in a comparative study between Belgium and Korea.