The use of tympanic thermometry is attractive in primary care, but a recent systematic review highlighted the paucity of data comparing tympanic thermometry with conventional methods. We report a study of 94 preschool children presenting to primary care in the United Kingdom (UK) with acute cough in whom tympanic infrared and axillary mercury thermometry are compared. Infrared thermometry showed poor agreement, poor sensitivity and high specificity. Infrared thermometry is too insensitive to be used as a screening test for fever, but when fever is already suspected, for example by touch, it may be useful as a 'rule in' test.