We evaluated the demographic, medical, and flight characteristics of 1,115 passengers who were routinely referred for preflight medical screening by a major domestic air carrier. The largest category consisted of 892 patients who requested in-flight oxygen therapy for cardiopulmonary conditions, of which COPD and cardiac disorders were the most frequent indications; 561 of these patients were 60 years or older. Overall, 386 passengers were recently hospitalized, 911 were using medications, 657 were receiving oxygen therapy, and 761 had flown previously. In the group using in-flight oxygen therapy, the average flight duration was 236 min and layover time, 87 min. These findings indicate that large numbers of patients undergoing preflight screening are receiving medication and have a wide range of medical diagnoses and variable health status. We conclude that preflight medical screening and counselling can be important and helpful in assuring safe and comfortable air travel in this patient population.