Background: In Denmark, Omalizumab is approved to treat children with severe persistent allergic asthma older than 6 years of age. No systematic registration of the efficacy in the Danish child population according to asthma symptoms or of the efficacy on co-morbid allergic symptoms exists. Results from a pilot study show that a broad panel of outcome measures is necessary to evaluate the efficacy of Omalizumab treatment as no change in lung function could be demonstrated Aim: To provide a standardized systematic registration in order to create a database enrolling children with severe allergic asthma treated with Omalizumab. Method and study design: A national multicenter registration and follow-up study based on children with clinical persistent severe allergic asthma including both retrospective and prospective registration. Inclusion criteria: • 6-18 years of age. • Severe persistent allergic asthma according to GINA treated with Omalizumab • Total serum IgE >? • Planned and accepted off-label treatment Outcome registration: A broad panel of outcome measures is scheduled at baseline and during treatment: Outcomes: • Asthma exacerbations • Hospitalizations • Medication • Lung function • ACT score • Peak-flow • FeNO • Mannitol/Methacholin test • Tolerable dose of allergen (oral allergen provocation) • Skin prick-test • Total serum IgE • Specific IgE • Quality of life score. (Juniper) • Rhinitis score, R-RTSS • SCORAD score The Follow-up programme (after ?) will be presented in a flowchart. Conclusion: We believe that a national systematic registration would improve sufficient data collection and increase knowledge regarding efficacy of Omalizumab treatment in this rare group of severe allergic asthmatic children.