Twenty-nine patients with severe chronic obstructive pulmonary disease (COPD) on long-term oxygen therapy (LTOT) were prospectively studied for compliance with therapy. Seven patients (24%) used oxygen < 16 hours/day and their mean 24-hour pulse oximetry showed mild hypoxaemia. In addition, we found that eight patients (28%) were smokers. We suggest that the follow-up of these patients should focus on the daily duration of the use of oxygen and cessation of smoking to optimise the effect of this therapy.