Abstract. Fever plays an important role in fighting infections, and although it can be inconvenient, it does not require treatment in a child who does not have other diseases. Some studies even show that lowering the temperature can prolong some diseases. However, fever increases the metabolic rate and the load on the cardiopulmonary system. Thus, fever can be harmful to children with pulmonary or cardiac risks or neurological disorders. It can also be a catalyst for febrile seizures, which, as a rule, although benign, cause very great concern among parents and should also be differentiated from more serious diseases (for example, meningitis). In children, the ability to regulate the thermal balance of the body is relatively weak, so it is easier for them to overheat or hypothermia of the body than in adults. The main reason for this is the insufficient development of the nervous mechanisms of regulation of thermal balance and, first of all, vascular reactions. Premature infants are unable to maintain their temperature homeostasis and react to ambient temperature as poikilothermic.