Fever, commonly defined by a temperature of >or=38.3 degrees C (101 degrees F), occurs in approximately one half of patients admitted to intensive care units. Fever may be attributed to both infectious and noninfectious causes, and its development in critically ill adult medical patients is associated with an increased risk for death. Although it is widespread and clinically accepted practice to therapeutically lower temperature in patients with hyperthermic syndromes, patients with marked hyperpyrexia, and selected populations such as those with neurologic impairment, it is controversial whether most medical patients with moderate degrees of fever should be treated with antipyretic or direct cooling therapies. Although treatment of fever may improve patient comfort and reduce metabolic demand, fever is a normal adaptive response to infection and its suppression is potentially harmful. Clinical trials specifically comparing fever management strategies in neurologically intact critically ill medical patients are needed.