UNLABELLED: Hyperthermia is characterized by an increase of body core temperature due to exogenous heat exposure and/or endogenous heat production. Contrary to fever the hypothalamic-controlled temperature set point remains unchanged. AIM: To demonstrate that exercise-induced hyperthermia is a common phenomenon in childhood. CASE: We describe a 5-year-old boy, who attended our outpatient clinic with a 6-month observation period of exercise-induced hyperthermia with rectal temperatures up to 39.0 degrees C. Characteristically temperature dropped to normal values after cessation of exercise. METHOD: In eight children aged 5-8, tympanic and rectal temperatures were measured before and after exercise. RESULTS: The rectal temperature increases frequently after exercise (p < 0.001), whereas tympanic temperature did not (p = 0.2). CONCLUSION: Benign hyperthermia should be considered in children with increased body temperature of unknown sources. The site of temperature measurement might be critical in the identification of this condition.