Pneumatic tourniquets, often used to provide a bloodless operating field, carry a risk of adverse effects. Limb exsanguination by gravitation is less aggressive than by mechanical means. Skin, muscles, nerves and vessels suffer maximally under tourniquet because of mechanical pressure, with both a sagittal force, responsible for compression and an axial force responsible for stretchening. All parts of the limb are therefore affected by ischaemia. The restarting of circulation will also increase lesions at the microcirculatory level, responsible for the "no reflow" phenomena. Transient reperfusion intervals are not necessarily beneficial. These effects will significantly contribute to the post tourniquet sensory motor injuries. The tourniquet increases the risk of sepsis. Tourniquet release allows metabolites from the leg to enter into the circulation, and also carries a risk of pulmonary thromboembolism. Carbon dioxide is eliminated by spontaneous hyperventilation under regional anaesthesia. If not eliminated by an increase of mechanical ventilation during general anaesthesia, it may raise intracranial pressure in head trauma patients. Various chemotactic and cytolytic agents may cause lung injury. Mobilization of blood volume at tourniquet placement and release may have detrimental haemodynamic effects in patients with coronary or cardiac insufficiency. The tourniquet increases arterial pressure after 20 to 25 minutes under general anaesthesia. Regional anaesthesia is considered as the technique of choice for the prevention of "tourniquet hypertension", closely linked to pain and relievable by local anaesthetics. Tourniquet modifies also the pharmacokinetics of anaesthetic and other agents. It generates hyperthermia, especially in children. Prospective and comparative studies did not show any advantage as far as duration of surgery and amount of blood loss are concerned. In order to minimize its side effects, the tourniquet must be used within the frame of a strict procedure, with a well adapted and regularly checked equipment. Duration of ischaemia should be as short as possible and not continue for more than two hours, with a reperfusion of 15 minutes every hour. Local hypothermia seems to be a safe means for decreasing side effects.