Introduction: Compare cost of the interstitial liquid glucose flash monitoring (FM) system (FreeStyle Libre 2) versus self-monitoring of blood glucose (SMBG) in adults with type 1 diabetes mellitus (T1DM) in Spain., Research Design and Methods: A model was developed to estimate, with the perspective of the Spanish health system, the annual costs associated with glucose monitoring and hypoglycemic events management in T1DM population, with multiple insulin daily doses (MDI). According to published evidence, rate of severe hypoglycemia (SHE) of 4.90 episodes per patient-year was applied. Reduction of SHE (58.6%) was modeled associated with FM use. Published rates of hospital care (20.2%) and subsequent admission (16%) were assumed for SHE. The daily consumption of strips and lancets was 9 in patients with SMBG (before and after 4 daily intakes and at bedtime) and 0.5 for FM users (according to IMPACT trial findings). Annual consumption of 26 FM sensors was considered (1 every 14 days). Unit costs (in € of 2019, excluding VAT) were obtained from literature and national databases. Sensitivity analyses (SA) were carried out to evaluate the model robustness., Results: The total annual cost/patient was €4437 for SMBG and €2526 for FM. The use of FM would be associated with an annual savings in the costs of monitoring and managing hypoglycemic events of €1911 per patient-year. In a hypothetical cohort of 1000 patients with T1DM MDI, FM could avoid in 1 year 4900 SHE, 93 hospitalizations for SHE. In addition, the use of FM would generate total savings of up to €1 910 000 per year. In the SA with alternative hypoglycemia events rates and use of strips and lancets, and including non-SHE episodes, savings from €370 000 to €1 760 000 were observed with FM., Conclusions: The use of the FM system to monitor glucose in adults with T1DM treated with MDI, would reduce hypoglycemic events and would result in cost savings for the health system., Competing Interests: Competing interests: Abbott Diabetes Care provided unconditioned financial support for performing the analysis. IO is an employee of PORIB, a consultant specialized in the economic evaluation of healthcare interventions, who provided technical and editorial support for conducting the study. FG-P, JFM-T, MB, FM-P, VB and RC-H received payment from Abbott Diabetes Care for consultant activities related to validation of the parameters and results. None of them received financial compensation for review and co-authorship of this manuscript. All the authors contributed to interpretation of the results and reviewed and approved the final version of the manuscript., (© Author(s) (or their employer(s)) 2020. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)