BACKGROUNDS: Various methods have been devised for choosing the correct internal diameter (ID) of endotracheal tubes and the proper lengths for oral endotracheal tubes at different ages in children. This study was performed to evaluate the appropriate sizes of uncuffed endotracheal tubes and distance from upper incisor to carina in Korean children under 8 years old. METHODS: Five hundred thirty five children under 8 years in ASA class 1 and 2 were evaluated for the study by age groups: 0~3 months, 4~11 months and every each year until 8 years. Appropriate sizes were to permit a gas leak at 15~25 cmH2O with positive pressure ventilation. Distances from incisor to carina were at the point which bilateral lung sounds were noticed during slow extubation from endobroncheal intubation. RESULTS: Appropriate tube sizes were 3.0 mm to 3.5 mm for infants under 3 months, 3.5 mm to 4.0 mm for 4 to 11 months and ""4.15+0.28xage (yr) (mm)"" (R2=0.77, p<0.05) for children between 1 and 8 years old. Distances from upper incisor to carina were 12.0 cm for infants under 3 months, 13.7 cm for 4 to 11 months and ""14.5+0.6xage (yr) (cm)"" (R2=0.62, p<0.05) for children between 1 and 8 years old. CONCLUSIONS: We conclude that the endotracheal tube ID for the Korean children are a little greater than those of previous reports in foreign countries and airway lengths for the Korean children are similar to those of foreigners.