Every day in the United States the airline industry boards over 1.7 million passengers for a total of 600 million passengers per year. As these passengers enter the cabin of their aircraft few are aware of the artificial environment that will protect them from the hazards of flight. Passengers are exposed to reduced atmospheric pressure, reduced available oxygen, noise, vibration, and are subject to below zero temperatures that are only a quarter inch away-the thickness of the aircraft's skin. Over the past decade there have been both technical and lay articles written on the perception of poor cabin air quality. Studies have, in part, supported some of those concerns, but, in general, the air quality exceeds that found in most enclosed spaces on terra firma. Since the events of September 11th, passengers have not only been exposed to the physical stress of flight, but also to social and emotional stress preceding departure. There has been a significant increase in air rage on board aircraft, which poses a threat to flight safety and a fear of harm to passengers and crew. The phrase "economy class syndrome" has received popular press attention and refers to the possibility of deep vein thrombosis (DVT) in the tight confines of an aircraft cabin. Studies have been conducted that demonstrate DVT can occur in flight just as it occurs in other modes of transportation or with prolonged sitting. In part, because of the stress related to commercial flight it is not a mode of transportation for everyone. Certain cardiovascular, pulmonary, and neuropsychiatric conditions are best left on the ground. Although medical problems and death are rare in flight, they do occur, and one major airline reported 1.52 medical diversions per billion revenue passenger miles flown. To provide medical support at 36,000 ft (11,000 m) most airlines now carry on-board medical kits as well as automatic external defibrillators. A recent survey conducted by a major airline revealed that there was at least one physician on 85% of all its flights. Both passenger and cargo aircraft have proven to be vectors of disease in that they transport humans, mosquitoes, and other insects and animals who, in turn, transmit disease. Transmission to other passengers has occurred with tuberculosis and influenza. Vectors for yellow fever, malaria, and dengue have been identified on aircraft. Although there are numerous health issues associated with air travel they pale in comparison to the enormous benefits to the traveler, to commerce, to international affairs, and to the public's health.