Acute upper airway obstruction presents an immediate threat to life. Following loss of the upper airway, hypoxemia with resultant cardiac arrest and death can ensue within minutes. Inspiratory stridor (a harsh, usually high–pitched sound) is the hallmark of upper airway obstruction. This is not to say, however, that upper airway obstruction cannot occur in the absence of stridor, because profound degrees of obstruction may manifest silently if airflow is nearly absent. When confronted with a child who has acute upper airway obstruction, the practitioner must assess the degree of obstruction quickly and accurately. The possibility of progression to complete airway obstruction with hypoxemia and cardiac arrest must be appreciated. Delaying intervention in a child whose airway is unstable may be costly, but unnecessary instrumentation in a child who has stable upper airway obstruction may precipitate a crisis.