Obesity results from a complex interaction of genetic and environmental factors and has reached epidemic dimensions in Germany. In addition to chronic overnutrition and lack of physical activity, psychosomatic aspects considerably contribute to the etiology, risk of complications, and extent of excess weight, at least in subgroups of obese patients. The basis of every treatment programme should be a combination of a moderately hypocaloric diet, increased physical activity, and behaviour modification. Although this programme is potentially effective for patients with severe or class III obesity, there is increasing use of surgical interventions. Although bariatric surgery produces substantial weight loss and is increasingly recommended, it should be offered only in centers providing multiprofessional care and psychosomatic expertise.