Elderly populations are prone to both hyperthermia and hypothermia because of innate physiologic changes associated with aging, the presence of chronic disease, and the use of polypharmacy. Hyperthermia is a true medical emergency with a high mortality rate, requiring rapid cooling and aggressive supportive care. Hypothermia is a common finding in elderly persons. Patients should be warmed in the least aggressive manner that will adequately treat their clinical situation. Hypothermia due to underlying disease carries a high mortality rate, as does the onset of ventricular fibrillation.