Within the last decade the use of non-invasive ventilation has expanded. This article reviews the studies on non-invasive ventilation in the treatment of exacerbations of chronic obstructive pulmonary disease (COPD), cardiogenic pulmonary oedema, acute respiratory distress syndrome, asthma and neuromuscular disease. Its beneficial effect has primarily been found in exacerbations of COPD where it reduces mortality with a number needed to treat of ten when added to standard medical treatment. No other conclusive evidence of the superiority of non-invasive ventilation compared to other modalities has been shown.