OBJECTIVES: To determine the cost-effectiveness of adding omalizumab to standard therapy (ST) in patients with uncontrolled severe allergic asthma, from the perspective of the Brazilian private health care system. METHODS: The cost-effectiveness analysis was based on Markov modeling, and estimated the costs and clinical outcomes, in a lifetime horizon, associated with ST with and without omalizumab add-on therapy. Clinical outcomes were expressed as clinically significant exacerbations (CSE) and clinically significant severe exacerbations (CSSE), according to the results of the phase III INNOVATE trial. Average doses, resource utilization per exacerbation, and omalizumab response rates were also obtained from the INNOVATE trial. Only direct costs were considered, including the acquisition costs of omalizumab and the costs of health care consumption related to exacerbations and routine visits. These costs were calculated from the perspective of the private healthcare payer. In the model, subjects transitioned between daily symptoms (optimized asthma control) and CSE or CSSE states, reflecting the clinical course of severe asthma.  Patients could have several sequential CSE, or could remain exacerbation-free for prolonged periods, as determined by transition probabilities. Death states were separated into death from all causes, and death due to severe asthma exacerbation. One-way sensitivity-analysis (OWSA) was performed to assess model robustness. Costs and clinical outcomes were yearly discounted at 5%. RESULTS: The base-case analysis showed that in comparison with ST alone, the use of omalizumab+ST resulted in less exacerbations per patient (17.57 CSE and 9.27 CSSE avoided) at an additional cost of BRL163,190 (BRL1=USD0.492). Therefore, omalizumab ICERs were BRL9,289/CSE avoided and BRL17,597/CSSE avoided. OWSA confirmed the favorable results of the base-case for omalizumab. CONCLUSIONS: Considering the parameters applied, from the Brazilian private health care system perspective, omalizumab add-on therapy is very cost effective compared with ST alone in the treatment of patients with uncontrolled severe allergic asthma, costing less than the WHO threshold of 1GDP per capita (BRL21,252).