Accidental hypothermia is defined as an unintentional decline in the core temperature below 35 °C. At this temperature, the coordinated systems responsible for thermoregulation begin to fail, since the compensatory physiologic responses to minimize heat loss through radiation, conduction, convection, respiration, and evaporation are very limited.1–4 In this article, we shall present an overview of the pertinent pathophysiology and guidelines for resuscitation and rewarming. Nuclei in the preoptic anterior hypothalamus coordinate heat conservation. Activation of these thermostats and the cutaneous cold receptors initiates a cascade of compensatory physiologic events (Table 1). After the initial stimulus, there is progressive depression. . . © 1994, Massachusetts Medical Society. All rights reserved.