Rift Valley fever probably occurred in East and South Africa for many years, where it occasionally caused sever epizootics among sheep and to a less extent in cattle and goats. Particularly newborn animals fall victims to the disease, whereas the majority of pregnant ewes and cows abort. In recent years, the disease spread to the Sudan and reached the Nile delta in 1977, where it not only caused an epizootic but also an epidemic among the population, resulting in approximately 18,000 cases and nearly 600 deaths. During the summer of 1978, the disease was observed again so that the virus must have overwintered in the newly infested area. The disease in animals and subsequently in man, displaying four different clinical forms, is discussed. The limited knowledge of the pathogenesis and epidemiology is stressed particular attention being paid to the Egyptian epizootic and epidemic. Because of inadequate knowledge of the clinical features, pathogenesis and other data, the disease among cattle was not detected until from five to six months after it had broken out. The spread of Rift Valley fever to the north-eastern part of Africa forms a potential threat of dissemination of the virus to neighbouring countries, situated on the two adjacent continents of Asia and Europe, and it is a real one. International travel and movement of goods and animals as well as the political situation in that area involves the danger of the Rift Valley fever virus also being transferred to new areas and becoming established there.