The classification of airway stenoses has been a problem for many years. As a result, both intradepartmental and interdepartmental comparisons of airway sizes remain difficult. It follows that comparisons of therapeutic maneuvers are even more difficult. A system is proposed that is simple, reproducible, and based on a readily available reference standard. Endotracheal tubes, which are manufactured to high standards of precision and accuracy, can be used to determine the size of an obstructed airway at its smallest point. The endotracheal tube that will pass through the lumen, if one exists, and tolerate normal leak pressures (10 to 25 cm H2O), can be compared to the expected age-appropriate endotracheal tube size. By using the outside diameters of the endotracheal tubes, the maximum percentage of airway obstruction can be determined. We present a conversion of tube size to the proposed grading scale: grade I up to 50% obstruction, grade II from 51% to 70%, and grade III above 70% with any detectable lumen. An airway with no lumen is assigned to grade IV.