While inadvertent perioperative hypothermia has received serious attention in many surgical specialties, few discussions of hypothermia have been published in the plastic surgery literature. This article reviews the physiology of thermoregulation, describes how both general and regional anesthesia alter the normal thermoregulatory mechanisms, indicates risk factors particularly associated with hypothermia, and discusses the most effective current methods for maintaining normothermia. Hypothermia is typically defined as a core body temperature of </=36 degrees C (</=96.8 degrees F), though patient outcomes are reportedly better when a temperature of >/=36.5 degrees C is maintained. Unless preventive measures are instituted, inadvertent hypothermia occurs in 50% to 90% of surgical patients, even those undergoing relatively short procedures lasting one to one-and-a-half hours. During either general or regional anesthesia, a patient's natural behavioral and autonomic responses to cold are unavailable or impaired, and the combination of general and neuraxial anesthesia produces the highest risk for inadvertent perioperative hypothermia. Unless hypothermia is prevented, the restoration of normothermia can take more than 4 hours once anesthesia is stopped. Consequences of hypothermia are serious and affect surgical outcomes in plastic surgery patients. Potential complications include morbid cardiac events, coagulation disorders and blood loss, increased incidence of surgical wound infection, postoperative shivering, longer hospital stays, and increased costs associated with surgery. Measures for preventing hypothermia are emphasized in this article, especially those proven most effective in prospective and controlled clinical studies. Perhaps the most important step in maintaining normothermia is to prewarm patients in the preoperative area with forced-air heating systems. Intraoperative warming with forced-air and fluid warming are also essential. Other strategies include maintaining an ambient operating room temperature of approximately 73 degrees F (22.8 degrees C), covering as much of the body surface as possible, and aggressively treating postoperative shivering. None of these measures can be adequately employed unless a patient's core body temperature is monitored throughout the perioperative period. Prevention of perioperative hypothermia is neither difficult nor expensive. Proper preventive measures can reduce the risk of complications and adverse outcomes, and eliminate hours of needless pain and misery for our patients.