Obese subjects are at a high risk of cardiovascular, respiratory and thromboembolic diseases. Anaesthetists in charge of these patients must take this risk into account, along with technical problems such as difficult venous punctures and intubations. The supine position alone creates situations that can be catastrophic for the respiratory and cardiac functions. In addition, obesity may modify the pharmacokinetics of the often liposoluble drugs used in anaesthesia. From the preoperative to the postoperative phases the anaesthetist's intervention must be envisaged.