The first aerial wildlife census of the entire 15,000-square-mile Serengeti--Mara region of East Africa was conducted between May 18 and 31, 1961. Careful counts were made of wildebeests (Gorgon taurinus) and zebras (Equus burchelli); final totals were 239,516 and 171,873, respectively. Less detailed counts or estimates were made of other species: buffaloes (Syncerus caffer), 21,832; elands (Taurotragus oryx), 6,400-9,600; elephants (Loxodonta africana), 1,157; hartebeests (Alcelaphus buselaphus), 2,100+; lions (Panthera leo), 550-700; black rhinoceroses (Diceros bicornis), 83+; topis (Damaliscus lunatus), 19,877; and Thomson's gazelles (Gazella thomsonii), 480,000-800,000. Slow, high-winged monoplanes were used, at elevations of 400-700 feet, flying 1- to 5-mile-long parallel strips, with the authors counting 150-400 yards on either side. Large herds were counted from color photographs. Maps of species distribution, topography, and vegetation are presented. The significance of the census results to research and management is discussed, and previous counts from parts of the area are reviewed. The census confirmed that a significant irregular interchange of zebras and wildebeests occurs between the Kenya and Tanganyika areas. The seasonal wildlife migration was shown to be an irregular dispersion over a vast area of animals apparently following available supplies of water and preferred food. Royal Air Force photographs of the major game concentrations provided a check on the accuracy of the census.