OBJECTIVES: The first objective was to assess the two-year changes in quality of life after gastric bypass in patients with severe obesity. Second, we analysed the effect of weight reduction on the different HRQL dimensions in the framework of the International Classification of Functioning, Disability and Health (ICF). METHODS: We carried out a prospective intervention study with consecutive patients referred to two bariatric surgical units in the Basque Country. We included generic (SF-36, EuroQuol 5D) and specific questionnaires (Moorehead-Ardelt, Obesity-related Problems scale). The SF-36 mental and physical dimensions and stigma theory, allowed us to apply an approach based on the ICF. We measured effect size (ES), standardized response mean (SRM) and ROC curves. RESULTS: Of 82 operated patients, 79 were tracked for 2 years. Average weight loss was 49 kg (28%) and BMI was reduced from 50.6 to 31.8. The initial problems and the final improvements were larger in the physical dimensions. The benefit of treatment was large for almost all HRQL domains as measured by EQ-5D, SF-36, OP and Moorehead-Ardelt. Only the improvements in some of the mental domains of the SF-36 were classified as small or moderate. ROC curves were not sensitive to change in BMI. CONCLUSIONS: We suggest that the negative impact of severe obesity on HRQL is mainly a cause of disability as described in the ICF. Two-year improvements in HRQL are related to recovery from disability after gastric bypass treatment. The primary focus on the physical dimension is not contradictory with evidence of the impact of weight-related stigmatization in obese individuals at the social level and its consequences in mental health. In the ICF framework,