Obesity is becoming a major public health problem throughout the world. It is now the second leading cause of death in the United States and is associated with significant, potentially life-threatening co-morbidities. Significant advances in the understanding of the physiology of body weight regulation and the pathogenesis of obesity have been achieved. A better understanding of the physiology of appetite control has enabled advances in the medical and surgical treatment of obesity. Visceral or abdominal obesity is associated with an increased risk of cardiovascular disease and type 2 diabetes. Various drugs are used in the treatment of mild obesity but they are associated with adverse effects. Surgery has become an essential part of the treatment of morbid obesity, notwithstanding the potential adverse events that accompany it. An appreciation of these problems is essential to the anaesthetist and intensivist involved in the management of this group of patients.