Severely obese patients affected by two or more chronic conditions which could mutually influence their outcome and disability can be defined as "complex" patients. The presence of multiple comorbidities often represents an obstacle for being admitted to clinical settings for the treatment of metabolic diseases. On the other hand, clinical Units with optimal standards for the treatment of pathological conditions in normal-weight patients are often structurally and technologically inadequate for the care of patients with extreme obesity. The aims of this review paper were to review the intrinsic (anthropometrics, body composition) and extrinsic (comorbidities) determinants of disability in obese patients and to provide an up-to-date definition of hospital-based multidisciplinary rehabilitation programs for severely obese patients with comorbidities. Rehabilitation of such patients require a here-and-now multidimensional, comprehensive approach, where the intensity of rehabilitative treatments depends on the disability level and severity of comorbidities and consists of the simultaneous provision of physiotherapy, diet and nutritional support, psychological counselling, adapted physical activity, specific nursing in hospitals with appropriate organizational and structural competences.