In children with a malignant mediastinal lymphoma, acute respiratory occlusion can be a life-threatening complication during general anaesthesia. 26 cases have been reported since 1973, with five deaths. There were 23 boys for 3 girls, aged between 13 months and 18 years. The hazards of anaesthesia in these children are described. The risk of airway obstruction should be assessed preoperatively. General anaesthesia, carried out with the patient half-sitting, should be aimed at maintaining spontaneous breathing, and therefore muscle relaxants should be avoided. The anaesthetist should also be prepared to change the patient rapidly to a lateral or prone position; a rigid bronchoscope should always be at hand. Preoperative awareness of the risk of respiratory occlusion in these patients is essential so that the correct anaesthetic technique can be chosen and the postoperative course prepared.