Decompression sickness (DCS) is a disease caused primarily by bubbles formed from dissolved gas in blood and/or tissue following a reduction in ambient pressure. It is most commonly seen in divers after surfacing, but it may also occur in aviators ascending to altitude in unpressurized or semi-pressurized aircraft or in astronauts decompressing for space walks. DCS is a puzzling, variable and to some extent unpredictable disorder with a wide range of potential presentations. At one extreme it may be rapidly fatal, whereas at the other it may manifest with mild, non-specific symptoms. Perhaps not surprisingly, it is the most widely recognized medical complication of diving and the subject of much interest among divers and diving physicians alike.