We prospectively assessed common clinical endpoints for their usefulness in avoiding hyperinflation of the cuffs of laryngeal mask airways (slight outward movement) and tracheal tubes (disappearance of an audible leak around the cuff during manual ventilation < 20 cmH2O) in 640 children. Cuff pressures were measured at induction and immediately before emergence from anaesthesia. With the laryngeal mask airway (sizes 1–4), the median cuff pressures ranged from 90 to > 120 cmH2O at induction and 105 to > 120 cmH2O before emergence. With tracheal tubes (sizes 3–7 mm), median cuff pressures were 40–60 cmH2O at induction and 45–70 cmH2O at emergence. With the use of nitrous oxide a consistent rise in cuff pressure was observed between the first and second readings whereas cuff pressures remained constant when nitrous oxide was not used. The use of clinical endpoints alone was associated with significant hyperinflation of cuffs with both devices in almost all patients, with an exacerbation when nitrous oxide was used. In order to avoid unnecessary cuff hyperinflation in laryngeal mask airways and tracheal tubes, the routine use of cuff manometers is mandatory in children.