IntroductionObesity surgery is the best treatment for extreme obesity, with demonstrated long-term positive outcomes. The potential cost-savings generated by the improvement of comorbidities after surgery can justify the allocation of more resources in the surgical treatment of obesity. MethodsThis was an observational, descriptive, longitudinal and retrospective study. Eligible patients underwent Roux-en-Y gastric bypass surgery at the Hospital Universitario Central de Asturias between 2003 and 2012. The established minimum follow-up period was two years. We calculated the individualized cost per patient treated (bottom-up) as well as per Diagnosis-Related Group (DRG) codes (top-down). ResultsOur study included 307 patients. The average cost per hospitalization calculated by DRG codes was €6545.90, and the average cost per patient was €10572.20. DRG 288 represented 91% of the series, with a value of €4631. The number of medications also decreased during this period, from 2.86 to 0.78 per medically treated patient, representing a cost reduction of €4433 per patient with all the obesity-related comorbidities analyzed. ConclusionsTwo years after Roux-en-Y gastric bypass conducted at Hospital Universitario Central de Asturias, the savings in drug costs for patients with multiple pathologies would compensate the inherent costs of the surgical treatment itself. Our results showed that DRG-related costs were insufficient to make a correct economic evaluation, so we recommend an individualized cost calculating method.