Body temperature measurement is most commonly taken to confirm the presence or absence of fever. Many decisions concerning the investigation and treatment of children are based on the results of temperature measurement alone. Determining the presence of fever in young children is particularly important. A missed fever is serious, but a false-positive fever reading can result in unnecessary septic workups. The axillary, rectal, oral and tympanic membrane sites are most commonly used to record body temperature, and electronic and infrared thermometers are the devices most commonly used. Each site and device has numerous advantages and disadvantages, which are described in this article. The search for the means of measuring body temperature that best combines accuracy, speed, convenience, safety and cost-effectiveness goes on. The infrared thermometer and the tympanic site appear to offer such a combination. Electronic thermometers are also suitable when used orally or at the axilla in newborn babies.