Approximately 1 billion people travel each year by air on the many domestic and international airlines. On U.S. air carriers alone, it has been predicted that in the coming two decades, the number of passengers will double. A global increase in air travel, as well as a growing aged population in many countries, makes it reasonable to assume that there will be a significant increase in older passengers and passengers with illness. Because of a growing interest by the public of health issues associated with commercial flying, the Aerospace Medical Association prepared this monograph for interested air travelers. It is informational only and should not be interpreted by the reader as prescriptive. If the traveler has any questions about fitness to fly, it is recommended that he or she consult a physician. The authors sincerely hope that this publication will educate the traveler and contribute to safe and comfortable flight for passengers.