Anaesthesia for patients with mediastinal masses may be associated with significant respiratory and cardiovascular complications. In this review, we discuss the anatomical and pathological considerations in these adult and paediatric patients and the three types of intra-thoracic compromise that may be found: compression of the tracheobronchial tree, compression of the pulmonary artery and heart and the superior vena caval syndrome. Patient evaluation by symptom history, computerized tomography and flow-volume loops is emphasized. Preoperative thoracic radiation therapy in severely symptomatic patients is associated with a decrease in postoperative respiratory complications and an improvement in risk. During radiation therapy a small window can be created to spare some tissue for adequate histological diagnosis. Anaesthetic management techniques for these patients are discussed. Life-threatening complications can occur at any point during anaesthesia for patients with mediastinal masses. Anaesthetists should have a high degree of awareness of the underlying anatomy, pathophysiology and anaesthetic alternatives when caring for these patients.