Background and Aim: Disease control is not achieved in a substantial proportion of patients with asthma. Recent advances in aerosol formulations and delivery devices may offer more effective therapy. This review will focus on the importance and potential clinical benefit of targeting the lung periphery in adult asthma by means of ultrafine aerosols. Results: Ultrafine formulations of inhaled corticosteroids have improved lung deposition up to at least 50 %, primarily in the peripheral airways. Ultrafine formulations of ICS provide equivalent asthma control to non-ultrafine ICS at approximately half the daily dose with no increased risk of systemic effects. Clinical studies of adults with asthma have shown a greater effect of ultrafine ICS, compared with non-ultrafine ICS, on quality of life, small airway patency, and markers of pulmonary and systemic inflammation, but no difference with regard to conventional clinical indices of lung function and asthma control. Conclusions: Asthma patients treated with ultrafine ICS, compared with non-ultrafine ICS, have at least similar chance of achieving asthma control at a lower daily dose. Further clinical studies are needed to explore whether treatment with ultrafine formulations of ICS will change the natural history of asthma and prevent airway remodelling in both the large and small airways.