OBJECTIVES: To assess the budget impact generated by the use of Omalizumab in Caja Costarricense de Seguro Social (CCSS) and to estimate the cost effectiveness of the intervention in Costa Rica’s Social Security. METHODS: Based on the effectiveness study previously conducted, that demonstrated that giving treatment with omalizumab to patients with uncontrolled severe asthma in Costa Rica’s Social Security, significantly improves their clinical condition after 6 months, we collected information on the amount of units of Omalizumab bought and administered to patients. Then, we constructed a model (decision tree) to evaluate the cost of clinical management of a patient with sever asthma with and without Omalizumab, using effectiveness data in clinical practice documented in CCSS. Cost data for medicines was obtained from the price paid registered in CCSS database; hospitalization cost and Emergency Room (ER) attention costs were obtained from the CCSS institutional tariff model. RESULTS: Between January 2012 and December 2014, a total of 33 patients received omalizumab, with a total consumption of 1.571 units and an inversion of US$870.224,03. Last registered unit (vial with 150mg) price in December 2015 was US$553,93. In the base case scenario modeled, that considered a 4-day hospitalization time and 7-hour ER attention, the cost of treatment per patient without Omalizumab was US$14.526,4 and with Omalizumab it was US$13.779,5, saving US$747 using Omalizumab, with a cost-effectiveness ratio of US$633 per hospitalization avoided (cost saving technology). In the most pessimistic scenario in the sensitivity analysis conducted, that considered no hospitalizations avoided neither ER attentions avoided, there was an incremental cost of US$13.271,4, that represents about 1.31 times Costa Rica’s GDI per capita (US$10.100 in 2015). CONCLUSIONS: Considering effectiveness in clinical practice, omalizumab is a cost-saving technology when prescribed to patients with uncontrolled sever allergic asthma in Costa Rican Social Security.