Fever is an unspecific symptom of most intensive care patients during their stay on an intensive care unit. The reasons for the increase of body temperature often remain unclear, even extended diagnostic measures are performed. The pathogenetic relevance of fever is commonly underestimated and leads to unreflected treatment of every increase of body temperature above 38 C. But the development of fever in patients is quite often useful and should not be treated with antipyretics. Physical measures like ice packs and surface cooling are only allowed to be used, if the central set point is lower than the actual core body temperature. This gradient can be recognized, when the patient starts to sweat. Principally, the treatment of fever in cardiovascular risk patients, patients with high risk for adverse neurological outcome, pregnant women during the first trimenon and in children with seizures must start with pharmacological interventions,which can be followed by physical measures.