BACKGROUND: Obesity is a clinical condition that contributes to the development of related disability in different areas (physical, psychological and social). Multidisciplinary treatment calls for specific instruments able to evaluate all related functional problems. We have developed a tool (an ICF-based assessment instrument, the ICF-OB schedule) to evaluate obesity-related disability, composed of an inventory of 71-items from the WHO International Classification of Functioning, Disability and Health (ICF).AIM: The aim of the present study was to validate this new tool for the definition of obesity-related disability. We also sought to examine the relationship between obesity disability, an index of multimorbidity (Cumulative Illness Rating Scale, CIRS) and a well-validated score of perceived obesity-related disability (Italian Obesity Society Test for Obesity-Related Disability, TSD-OC).DESIGN: Process validation of the ICF-OB schedule.SETTING: Baseline conditions of out- and in-patients.POPULATION: A large cohort of obese patients recruited from 9 multidisciplinary Centers belonging to the Italian Obesity Society (SIO) network, which provide specialized obesity care.METHODS: A total of 353 patients (F: 70%, age: 50.2±12.7yrs, BMI: 41.4±8.3kg/m2) were enrolled between January 2017 and June 2018. The ICF-OB was used to define patients' functioning and disability profiles in order to set and appraise rehabilitation goals.RESULTS: We described the distribution of body functions (BF), body structures (BS) and activities and participations (A&P) categories and the agreement rates were significant for the majority of these. The ICF-OB was more often significantly associated, and with stronger coefficients, with patients' comorbidities as described by the CIRS rather than with body mass index (BMI). The TSD-OC also presented a strong association with A&P indexes.CONCLUSIONS: the complexity of clinical condition, that generates disability in obesity might be well identified with the use of this new instrument that appear significant related to the perceived disability for each patients and also with their multimorbidity.REHABILITATION IMPACT: The ICF-OB shows great promise as a tool for goal setting in the rehabilitation of obese patients.