Single lung transplantation can rarely become complicated by hypoxia, hypercarbia and haemodynamic instability which requires extracorporeal support in order to conduct the transplant safely. The decision to use cardiopulmonary bypass must be taken by the surgeon and anaesthetist together after assessing the circumstances but should then be executed without delay. The need for bypass can sometimes be predicted before surgery or becomes obvious most often after induction of anaesthesia or at the time of clamping the pulmonary artery. The use of cardiopulmonary bypass for single lung transplantation is becoming less frequent as its use becomes increasingly confined to patients who have deteriorated significantly on the waiting list or those who are older. Peripheral cannulation of the femoral artery and vein with transoesophageal echocardiographic guidance of venous cannula position and the use of venous assisted drainage allows for rapid institution of cardiopulmonary bypass and an unobstructed operative field in the thorax. Alternatively, cannulation of the main pulmonary artery can be used to effect venous drainage or direct cannulation of the right atrium can be used if the transplant is to be undertaken on that side. Left thoracotomy permits cannulation of the aortic arch or descending aorta for arterial return. Under conditions of cardiopulmonary bypass with modest hypothermia single lung transplantation can proceed in safety. Although many have suggested adverse outcomes when lung transplantation is undertaken with bypass, several series have not indicated high incidences of significant complications. The likelihood of needing bypass may be suggested preoperatively by low right ventricular ejection fraction and poor 6-min walk test results in patients with restrictive lung pathology. This allows the surgeon and anaesthetist to predict problems and be more prepared to intervene with extracorporeal circulation.