Background: Today asthma is one the most important chronic disorders in the developed world. Evidence from around the world shows that the prevalence of asthma has increased considerably since 1975, and it now affects around 5% of the world population (about 300 million individuals). In Norway, approximately 10-12% of Norwegian children and young adults and approximately 8% of adults are exposed by different stages and phenotypes of asthma. The basic treatment assumes different dozes of corticosteroids and different types of beta agonists depending on asthma severity. Still some group of patients experience bad asthma control and may require additional treatment. Today asthma has come no longer been considered as a single disease, but a collection of different conditions with overlapping symptomatology, but diverse etiologies. The importance of defining subtypes has been increasingly recognized and multiple subphenotypes of asthma have been identified based on clinical, functional or inflammatory parameters. For eosinophilic phenotype, it might be beneficial to use new kind of treatment that is called IL-5 inhibitors, a type of monoclonal antibodies therapy. Potential treatment approach assumes using IL-5 inhibitor as add-on treatment for common medication. Aim: This study is designed to compare the cost-effectiveness of common treatment alone and new IL-5 inhibitor, Reslizumab, as add-on treatment to common treatment for severe eosinophilic asthma patient group. Methods: A Markov model was developed with quality-adjusted life years (QALY) gains and costs per QALY as the outcome. Costs were considered from a healthcare perspective. To catch possible uncertainty around the model, a probabilistic sensitivity analysis was conducted. The expected value of perfect information was calculated. One-way sensitivity analysis was conducted to establish the boundary price of Reslizumab. Results: The incremental cost of Reslizumab is NOK 267 260; the incremental effect is 0,8 QALYs. Consequently, that gives us an incremental cost-effectiveness ratio (ICER) of NOK 339 386 given the Swedish price of NOK 4923. Using the UK estimated price of NOK 8282, the ICER is NOK 642 986. The highest price for cost-effectiveness of Reslizumab is NOK 6700 per one QALY. Conclusion: Reslizumab is cost-effective if the willingness to pay (WTP) per one QALY is NOK 350 000 or higher. At a lower level of WTP, common treatment alone is the cost-effective choice. Still additional research might be necessary to minimize uncertainties in the results.