A three-year-old boy is reported with severe upper respiratory tract obstruction and sleep apnoea that was associated with reversible pulmonary hypertension and cardiac enlargement, and relieved by emergency tonsillectomy. The importance of intermittent cyanosis and difficulty in arousal during the day are stressed, together with the risk of death from anaesthesia in such patients without full pre-operative assessment. Despite this risk, and the current climate of increasing reluctance to subject children to tonsillectomy, the operation is absolutely essential and potentially lifesaving in certain children such as the boy described.