We assessed the ability of mothers to subjectively determine the presence or absence of fever in their children when compared with simultaneous temperature determination obtained by thermometer. Mothers who said their children were febrile were correct 52.3% of the time; those who said their children were afebrile were correct 93.9% of the time. The sensitivity was 73.9% of the specificity was 85.6%. Ninety percent of children aged 2 years or younger with temperatures of 38.9 degrees C or higher were correctly identified as febrile. Administration of antipyretics to both febrile and afebrile children was greater among those whose temperature was determined at home by thermometer than among those whose temperature was determined by subjective criteria. We conclude that maternal subjective fever assessment criteria are useful as a screening method to rule out the presence of fever at all ages and that mothers can identify high fevers in most young children without the use of a thermometer.