The maintenance of thermal equilibrium depends on the normal functioning of numerous body systems and their appropriate interaction with the environment. Man has a complicated neural and neuroendocrine control system that is designed to maintain a constant core temperature despite changes in environmental temperature or level of activity. Heat exchange is a bidirectional process involving the transfer of heat between an object and its environment. There are four mechanisms of heat dissipation: evaporation, conduction, convection, and radiation. Heat production is the sum of basal metabolism and shivering and non-shivering thermogenesis. The hypothalamus is the central control centre that ensures thermal homeostasis. Although many schemes exist for the classification of hypothermia, from the clinical point of view it is recommended to consider any temperature below 35 degrees C significant. Accurate temperature measurement and core temperature monitoring are essential for diagnosing hypothermia.