Accidental hypothermia is an important clinical condition in emergency and disaster medicine. It is usually classified as mild, moderate, severe, or extreme (body temperature below 18-20 degrees C; no recordable EEG activity). However, exposure time, trauma, serious illness, or the effects of drugs or alcohol may both attenuate and complicate the clinical course. This paper describes exposure mechanisms, the pathophysiologic processes, the body's thermo-regulating mechanism and diagnostic criteria. The author also discusses choice of treatment in the acute stages, during transportation and in hospital. The treatment should take into account not only the degree of hypothermia, but also exposure time, state of consciousness, and complicating factors such as trauma, drugs or alcohol. When hypothermia is associated with cardiac arrest, rewarming by extracorporal support is recommended.