Recently, a well-designed crossover study assessed the risk of thrombosis during long flights.1,2 Included were persons with such risk factors as factor V Leiden mutation and oral contraceptive use. All 71 patients (15 men, 56 women) were studied (not randomized) in each limb of the protocol--in random order--during each of the following: an 8-hour flight, 8 hours spent watching movies, and 8 hours of typical daily living. Fifteen of the participants took oral contraceptives, 11 had the factor V Leiden mutation, and 15 had both risks.