The use of cuffed tracheal tubes in paediatric anaesthesia is now common. The use of nitrous oxide in anaesthesia risks excessive tracheal tube cuff pressures, as nitrous oxide can diffuse into the cuff during the course of surgery. The aim of this single-centre, prospective, randomised controlled trial was to compare the effect of saline versus air for the inflation of tracheal tube cuffs on the incidence of excessive intra-operative cuff pressure in children undergoing balanced anaesthesia with nitrous oxide. Children (age ≤ 16 y) were randomly allocated to receive either saline (saline group) or air (air group) to inflate the cuff of their tracheal tube. The pressure in the tracheal tube cuff was measured during surgery and brought down to the initial inflation level if it breached a safe limit (25 cmH2O). Post-extubation adverse respiratory events were noted. Data from 48 patients (24 in each group), aged 4 months to 16 y, were analysed. The requirement for reduction in intra-cuff pressure occurred in 1/24 patients in the saline group, compared with 16/24 patients in the air group (p < 0.001). The incidence of extubation-related adverse events was similar in the saline and air groups (15/24 vs. 13/24, respectively; p = 0.770). The use of saline to inflate the cuff of paediatric cuffed tubes reduces the incidence of high intra-cuff pressures during anaesthesia. This may provide a pragmatic extra safety barrier to help reduce the incidence of excessive tracheal cuff pressure when nitrous oxide is used during paediatric anaesthesia.