Hypoxaemia is a common complication of acute lower respiratory tract infections in children. In most developing countries, where the majority of deaths from pneumonia occur, facilities for early detection of hypoxaemia are lacking and oxygen is in short supply. This review examines the usefulness of different clinical signs and symptoms in the prediction of hypoxaemia associated with acute respiratory infections in children. Several respiratory signs were found to be associated with hypoxaemia. These include very fast breathing (with a respiratory rate of more than 60 or 70 breaths per minute), cyanosis, grunting, nasal flaring, chest retractions, head nodding and auscultatory signs, as well as signs of general depression of the child, such as inability to feed or lethargy. The sensitivity and specificity of these signs, as described in the reviewed studies, is presented, and combination rules are discussed. Through appropriate combination of several physical signs, which can be used by peripheral health workers and be taught to mothers, it is possible to predict hypoxaemia in children with acute respiratory tract infections with reasonable accuracy.