Hilar displacement is one of the significant sign of pulmonary volume change. The hilar height ratio(HHR) is avalue that express the normal position of a hilum in its hemithorax, and it is calculated by dividing the distance from the hilum to the lung apex by the distance from the hilum to the diaphragm. Didplacement of one hilum is usually easy to detect but both are displaced in the same direction especially, recognition is more difficult,Knowledge of normal HHR allows evaluation of hilar positional change even when the relative hilar positions ar not latered. The right hilum is positioned in lower half of the right hemithorax, while the left hilum is situated inthe upper half of left hemithorax. The difference of hilar height ratio according to age group is slight, butthere is significant difference between right-HHR and left-HHR. The value of right-HHR is 1.28±0.14, the valueof left-HHR is 0.88±0.09.