INTRODUCTION Bariatric surgery offers effective obesity treatment. The aim of this study was to evaluate the cost-effectiveness of bariatric surgery in Denmark from a third-party payer perspective in the mid- (ten years) and long-term (lifetime). METHODS A state-transition Markov model was developed in which patients may experience surgery, post-surgery complications, diabetes mellitus type 2, cardiovascular diseases or die. Transition probabilities, costs and utilities were informed by the literature. Three types of surgery were included: gastric bypass, sleeve gastrectomy and adjustable gastric banding. The impact of different surgical methods on BMI level was informed by the Danish Obesity Surgery Registry (Dansk Fedmekirurgiregister). RESULTS In the ten-year base-case analysis, bariatric surgery led to a cost increment of 19,332 DKK and generated an additional 1.1 quality-adjusted life years (QALYs). In the course of a lifetime, surgery leads to savings of 36,403 DKK, an additional 0.7 life years and 2.9 QALYs. Bariatric surgery was cost-effective at ten years with an incremental cost-effectiveness ratio of 17,818 DKK per QALY and was dominant over conservative management in the course of a lifetime. Up to three years of delay in the provision of surgery resulted in a reduction of life years, a lower QALY gain and a minor decrease in healthcare costs. CONCLUSIONS In Denmark, bariatric surgery is cost-effective at ten years and may produce a significant reduction in healthcare costs over the course of a lifetime in persons with severe obesity. FUNDING Synergus AB received support for economic model development from Covidien AG (now part of Medtronic). TRIAL REGISTRATION not relevant.