Prescriptions of LTOT in non-COPD diseases vary from 20% to 60% of the total number of patients profiting from this form of treatment. It seems that in countries where the percentage of non-COPD indications is still high, the proportions will change toward higher use of LTOT in COPD patients in the near future. There is a death of controlled studies evaluating the effects of LTOT in non-COPD diseases. There are at least two important factors preventing realization of such studies. First, non-COPD indications for LTOT encompass a large number of diseases. Each of them should be separately studied because of differences in the pathophysiological mechanisms and natural history of the diseases. Small numbers of patients with a specific diagnosis would require multicenter, international studies, which are difficult to perform in a rigorous manner. A more important handicap is ethical reasons. Many years ago LTOT was approved as a routine method of treatment for severe stable hypoxemia. It would be difficult to obtain the approval of any ethics committee for a project proposing a control group of hypoxemic patients to be deprived of oxygen for a long period of time. It would also be difficult to find clinicians eager to participate in such a study. Do we need such studies at all, even in an era of evidence-based medicine? Probably not for diseases presenting with airway obstruction such as CF or bronchopulmonary dysplasia. The effects of LTOT in COPD may also be applied to those diseases. But there remains a group of diseases with restrictive patterns of ventilatory impairment. A typical feature of these diseases is a severe decrease in arterial oxygen tension and saturation during exercise. Oxygen supplementation during exercise has already been found to relieve hypoxemia and to increase exercise capacity. Life is motion. Perhaps we should not bother too much about prolongation of the life of our patients, which would be difficult to prove anyway. We should rather concentrate on assuring them as much mobility and enjoyment of life as possible. In other words we should work on adding life to years rather than adding years to life. For this, ambulatory oxygen is the best option.