Obesity poses a serious health hazard and its treatment is often disappointing. Major advances have been made during recent years in the understanding of body weight regulation, with the discovery of leptin, a protein produced by adipocytes and acting on the central nervous system to reduce food intake, and that of beta-3 adrenergic receptors and uncoupling proteins which contribute to stimulate energy expenditure. Numerous metabolic complications are associated with abdominal obesity and most of them, such as diabetes mellitus, dyslipidaemias and arterial hypertension, appear to be linked to insulin resistance and may be part of the socalled metabolic syndrome or syndrome X. While very-low-calorie diets are usually effective in the short-term, they cannot, in the long-term and for most patients, solve the problem of severe obesity. Pharmacological antiobesity treatment may include drugs that reduce food intake, drugs that increase energy expenditure and drugs that affect nutrient partitioning or metabolism. All of these pharmacological approaches have potential efficacy, but unfortunately serious limitations. This is also the case of mechanical means, such as intragastric balloons. Consequently, bariatric surgery may be considered as a valuable alternative therapy in well-selected patients with morbid obesity refractory to classical treatments. In conclusion, obesity is a chronic disease and should be treated as such with reasonable expectations.