Mediastinal masses can cause both cardiac and respiratory embarrassment because of pressure on the airway, the heart and its great vessels. These effects may be exacerbated by many factors in the peri-operative period and there is a high morbidity and mortality associated with anaesthesia in these patients. "0 Anaesthesia causes a reduction in lung volume, which compounds the pressure effects due to a mediastinal mass. We describe three children with mediastinal masses to illustrate how cardiac and respiratory problems may arise and suggest methods for prevention and management.