Infectious causes of airway obstruction can be distinguished by anatomic location and causative agent. Epiglottitis, the most common supraglottic obstruction, is bacterial in origin. An artificial airway and antibiotic therapy are mandatory. Spasmodic croup is a mild, transitory subglottic swelling which responds to mist and sometimes antihistamine therapy. Laryngotracheitis, or viral croup, affects the subglottic airway with fluctuating severity and is treated with mist, racemic epinephrine, oxygen, and sometimes steroids. Obstruction may be so severe that intubation or tracheostomy is needed. Laryngotracheobronohitis is the downward extension of viral croup, frequently accompanied by bacterial superinfection. Antibiotics may be needed, and airway intervention is more likely to be indicated than it is for uncomplicated viral croup. Bacterial tracheitis is a primary bacterial infection which causes thick secretions and membrane formation. Antibiotic therapy and sometimes airway intervention are needed. Diphtheria is a bacterial infection with toxin production, the treatment of which always includes both antitoxin and antibiotic and, sometimes, an artificial airway.