Transient mild hypothermia (core body temperature 35-32°C) is common and usually without consequences for the brain or other organs. However, prolonged severe accidental hypothermia (core body temperature below 28°C) due to accidents is rare, and usually fatal in more than 50% of cases. Little is known on its physiopathology, on prognostic factors for rewarming decision or ideal rewarming techniques for better survival. Furthermore, complications after successful rewarming are extremely frequent and very often severe or fatal. Accidental hypothermia is a frequent problem during the winter months and can be caused by snow sport accidents, near drowning and urban cold exposure. The International Hypothermia Registry's principle goal is to increase knowledge on accidental hypothermia by creating the largest database on accidental hypothermia which will comprise enough patient data to give a statistical power since the causes of accidental hypothermia and its treatment varies greatly. The International Hypothermia Registry (IHR) will enable improvement of pre- and in-hospital treatment and rewarming methods, study survival predictors and prevention of post-rewarming complications. By this way, the IHR will permit the establishment of evidence-based diagnosis and treatment guidelines.