Post-intubation croup and tidal volme leak during ventilator support may occur when unsuitable size of endotracheal tube is used. Malposition of endotracheal tubes(ETT) are particularly common in pediatric ICU patients, and may lead to serious complications such as inadvertent endobronchial intubation and accidental extubation. Due to the inaccuracy of physical examination for ETT placement and although there is additional time consumption and expense, the chest X-ray is still considered the gold standard for ETT position evaluation. We assessed the predetermined endotracheal tube size and the distance from the incisor to the carina according to the patient's age, weight and height. The chest X-ray was used for evaluation of these patients who were admitted to the intensive care unit of Severance Hospital Yonsei Medical Center from March to August, 1990. We divided the 430 intubated patients into two groups. Group 1 included 163 patents who were intubated by a endotracheal tube without a cuff. Group 2 included 237 patients who were intubated by a endotracheal tube with a cuff. The conclusion from our results were as follows: 1) The coefficient of determination of the endotracheal tube size, R(2), was highest according to weight, 0.40 and 0.50 in Group 1 and 2. The regression equation of endotracheal tube size using weight was Y=0.11X+3.42 and Y=0.04X+5.46 in Group 1 and Group 2. 2) The coefficient of determination of the distance from the incisor to the carina was highest according to weight 0.57 and 0.33 in Group I and 2. The regression equation of the distance from the incisor to the carina using weight was Y=0.47+10.74 and Y=0.11X+20.17.