Hypothermia influences body functions in many positive and negative ways. Hypothermia may be purposely induced during neurological or cardiac surgery for its cerebral protectant effects. However, hypothermia during the perioperative period is often detrimental, leading to increased bleeding and blood product utilization, as well as prolonged stays in the PACU. This article presents an overview of the physiology of temperature regulation and risk factors for the development of perioperative hypothermia. The effects of hypothermia on various body systems also are discussed and perioperative concerns explored.