Spirometry is an easy method to measure lung function and to show pathophysiology. It assists not only to determine the severity of bronchial obstruction in asthma but also to differentiate the characteristics of the intrathoracic diseases narrowing the central airways. Different types of benign and malignant tumors of the trachea may cause emergence of symptoms of airway obstruction. Herein a patient who had been initially diagnosed with asthma but later on shown to have intratracheal myofibroblastic tumor is presented. The importance of flow-volume curve in both initial diagnosis of the mass and in the detection of recurrence is discussed.