Infantile tracheomalacia is a potentially life-threatening disease requiring prolonged artificial respiratory support. Diagnosis and management of this disease may be further improved by establishing a suitable objective and quantitative assessment protocol for tracheal collapsibility. It is our hypothesis that tracheal collapsibility can be represented by the relationship between intraluminal pressure and cross-sectional area of the trachea. To test this hypothesis, static pressure/area relationships of the trachea were obtained from anesthetized and paralyzed infants, diagnosed as tracheomalacia by endoscopic observation, and fitted these values on a linear regression model, followed by calculation of the estimated tracheal closing pressure (P'close). P'close ranged from -8cmH2O to -27cmH2O, suggesting easy collapsibility of the trachea during crying or coughing, and non collapsibility during spontaneous respiratory cycle, which coincided with the infants' symptoms. It is our conclusion that tracheal collapsibility of infants with tracheomalacia can be quantitatively assessed by static pressure/area relationship of the trachea obtained under general anesthesia and paralysis.