Interest in the health and diseases of elderly people has been growing in most parts of the world during the last few decades. One reason is that knowledge of normal aging and of the manifestations of disease in the higher age groups has been incomplete compared to the corresponding knowledge regarding other periods of human life. Another reason is the increasing absolute and relative number of elderly not only in the developed, but also importantly in the developing world. It is estimated, for example, that the increase of the population aged 80 and over from 1980 to 2020 will amount to 108% in the developed world compared to 377% in the developing world (U.N. Department of International Economic and Social Affairs, 1985).