Recently there has been much interest in the use of hypothermia in the management of the brain-injured patient and its effect on outcome. Most of these studies examine the use of hypothermia compared with normothermia of 37°C and have failed to demonstrate a benefit in the treatment groups, but what is normothermia in the brain-injured patient? Good epidemiologic evidence suggests that the vast majority of patients admitted to an ICU environment will develop a fever. The development of fever is clearly associated with a worse prognosis. There is now a better understanding of the possible mechanism of harm of fever and the side effects of cooling. Several treatment options for controlling temperature are discussed. Despite a sound physiologic argument for controlling fever in the brain-injured patient, there is no evidence that doing so will improve outcome.