Accidental hypothermia is defined as an unintentional decline in the core temperature below 35 degrees C. The population of patients at risk is very heterogeneous. Common thermal stressors include both primary exposures and secondary contributory diseases or injuries. As the core temperature progressively declines, the compensatory metabolic, adrenergic, and cardiovascular responses that attempt to maintain thermal homeostasis fail. At this juncture, therapeutic intervention must occur. An understanding of the pathophysiological variables impacting rewarming is critical. For example, the effects of cold on the coagulation system impact both the approach to cardiovascular resuscitation and the choice of rewarming technique. There are no randomized controlled trials that definitively establish the ideal rewarming strategy for each unique presentation. The resuscitative goal is to match the clinical presentation with the threshold temperatures at which various rewarming modalities and pharmacological interventions should occur. Identification of the indications for both noninvasive and invasive active rewarming techniques in patients requiring critical care is key. Poikilothermia, failure to rewarm, endocrinologic insufficiency, cardiovascular instability, traumatic or toxicological induced peripheral vasodilation, or the presence of major predisposing factors mandates active rewarming. The simultaneous or sequential use of the various rewarming techniques permits a versatile approach to therapy. Outcome remains problematic to predict because there may never be a validated prognostic neurological scale. The history, physical examination, and, ironically, the vital signs are routinely misleading. A tachycardia that is not proportionate to the degree of hypothermia suggests hypovolemia, hypoglycemia, or the presence of toxins. Given the decreased carbon dioxide production, persistent hyperventilation implies an underlying organic acidosis or central nervous system abnormality. Finally, toxic or traumatic or infectious impairment of the central nervous system may be obscured by hypothermia.