BACKGROUND The prevalence of pneumothorax associated with travel in patients with interstitial lung diseases is unknown. In patients with lymphangioleiomyomatosis (LAM), in whom pneumothorax is common, patients are often concerned about the occurrence of a life-threatening event during air travel. The aim of this study was to determine the prevalence of pneumothorax associated with air travel in patients with LAM, idiopathic pulmonary fibrosis (IPF), and sarcoidosis. METHODS Records and imaging studies of 449 patients traveling to the National Institutes of Health were reviewed. RESULTS A total of 449 patients traveled 1,232 times; 299 by airplane (816 trips) and 150 by land (416 trips). Sixteen of 281 LAM patients arrived at their destination with a pneumothorax. In 5 patients, the diagnosis was made by chest roentgenogram, and in 11 patients by CT scans only. Of the 16 patients, 14 traveled by airplane and 2 by land. Seven of the 16 patients, 1 of whom traveled by train, had a new pneumothorax; 9 patients had chronic pneumothoraces. A new pneumothorax was more likely in patients with large cysts and more severe disease. The frequency of a new pneumothorax for LAM patients who traveled by airplane was 2.9% (1.1 per 100 flights) and by ground transportation, 1.3% (0.5 per 100 trips). No IPF (n = 76) or sarcoidosis (n = 92) patients presented with a pneumothorax. CONCLUSIONS In interstitial lung diseases with a high prevalence of spontaneous pneumothorax, there is a relatively low risk of pneumothorax following air travel. In LAM, the presence of a pneumothorax associated with air travel may be related to the high incidence of pneumothorax and not to travel itself.