Asthma is a chronic inflammatory disease, affecting up to 10 % of the general population in developed countries. Corticosteroids are necessary to control symptoms, but induce adverse events sometimes intolerable. In severe asthma, which represent 5 to 10% of global asthma, corticosteroids frequently fail to prevent severe exacerbations, leading to emergency care, hospitalization and sometimes death. The aim of this study is to identify predictive factors specific for exacerbation outcome which will lead to a minor increase in treatment in order to prevent exacerbations, while minimizing drug adverse effects.