OBJECTIVES: Obesity is a growing epidemic in Europe. The objective was to investigate the cost-effectiveness of bariatric surgery for obesity across four European countries. METHODS:  A Markov model was developed to compare the long-term (20 year) outcomes and costs for patients who receive bariatric surgery (gastric bypass, sleeve gastrectomy, adjustable gastric banding, duodenal switch) to those who receive diet and exercise programmes. The model was adapted for the German, French, Italian and UK healthcare systems. Body mass index (BMI) change, type II diabetes mellitus (T2DM), stroke, myocardial infarction, cancer, knee pain and sleep apnoea were included; inputs for these were taken from recent network meta-analyses. Utilities and costs were sourced from the literature and the healthcare system tariffs. The populations considered were patients with BMI≥40 or BMI≥35 with obesity-related comorbidities, and the subpopulation of T2DM patients. RESULTS: Compared to those receiving conventional care, patients undergoing bariatric surgery were found to live longer and have fewer cases of stroke, myocardial infarction, cancer, knee pain and sleep apnoea. Bariatric surgery was associated with an incremental cost-effectiveness ratio (ICER) of €125, €88 and £859 per quality-adjusted life year (QALY) gained versus conventional care for France, Italy and the UK, respectively. Bariatric surgery dominated conventional care in Germany, with cost savings per patient of €429 and QALY gains of 2.6. Bariatric surgery was associated with an ICER of less than €10,000/QALY in 100% of probabilistic simulations, for all countries. Differences between countries were driven by differences in the cost of surgery and treatment of comorbidities. Results were similar in the T2DM population. CONCLUSIONS: Bariatric surgery is predicted to improve patient outcomes and be highly cost-effective compared to diet and exercise programmes in all four European countries investigated. Further updates to the model are planned.