Objective: The aim of this feasibility study was to investigate the firstattempt success of ultrasonography (USG) in paediatric patients inpredicting an appropriate cuffed endotracheal tube (ETT) size.Methods: Fifty children who were 1-10 years of age and who receivedgeneral anaesthesia with endotracheal intubation for adenoidectomyor adenotonsillectomy were enrolled in the study. In all participants,the transverse diameter of the subglottic airway was measured withUSG at the cricoid level without ventilation. The outer diameter(OD) of the maximum allowable ETT was chosen according to themeasured subglottic airway diameter. In the presence of resistance topassage of the tube into the trachea or in the absence of an audibleleak at airway pressure of >25 cm H2O, the ETT was replaced witha tube whose internal diameter (ID) was 0.5 mm smaller. If a leakwas audible at airway pressures of <10 cm H2O, if a seal could notbe achieved with a cuff pressure of >25 cm H2O or if a peak airwaypressure of >25 cm H2O was observed during ventilation, the tubewas changed to a tube one size larger. The OD of the best-fit ETTwas converted to the ID. The best-fit ID, the requirement for ETTreplacement, the duration of airway diameter measurement by USGand the peak airway pressure were recorded.Results: The success rate of the first attempt with USG was 86%;the ETT was replaced in five patients with a tube one size largerand in two patients with a tube one size smaller.Conclusion: Our findings show the subglottic diameter measuredby USG to be a reliable predictor in estimating the appropriatepaediatric ETT size.