During 2007–2009 we conducted a survey of attacks by wild carnivores on the livestock of the Maasai and Sonjo tribes in the eastern Serengeti ecosystem of northern Tanzania. Local enumerators systematically recorded incidents of carnivore predation on livestock and their data were quantified by us, with the aid of District Game Officers or trusted local people. The annual rate of attack by African wild dogs Lycaon pictus was significantly higher (1.42 animals per 1,000 livestock) in the Sonjo tribal area than in the Maasai tribal area (0.72 animals per 1,000 livestock). In the Maasai tribal area there was a significant amount of predation by leopards Panthera pardus and spotted hyaenas Crocuta crocuta. In both tribal areas sheep Ovis aries and goats Capra aegagrus hircus were subject to predation more frequently than cattle. Attacks on livestock by wild dogs occurred most frequently in the afternoon and evening, whereas other carnivores generally attacked livestock at night. Sheep and goats were most frequently attacked by most carnivores during the long rainy season. Cattle Bos primigenius were most frequently attacked by wild dogs and leopards during the long dry season and by lions Panthera leo during the long rainy season, whereas spotted hyaenas killed cattle most frequently during the short rainy season.