This study assessed the difference in efficacy and patient morbidity when asthma drug therapy was administered by either a dry powder device (DPD) or metered dose inhaler (MDI). It assessed 27 patients who had used an MDI for at least six months before transferring to a DPD because of inadequate inhaler technique. Documentary evidence was collected retrospectively from the medical records six months before and six months after the change and outcomes were measured by daily bronchodilator therapy, daily inhaled steroid therapy, frequency of night-time wakening due to asthma symptoms, and peak expiratory flow rates. Patient symptoms and asthma control were found to be improved by the correct delivery of medication via a DPD compared with an MDI.