Laryngotracheobronchitis, as the name implies, refers to inflammation of the larynx, trachea, and bronchi. Cases of laryngotracheobronchitis can be more severe than laryngotracheitis as the former extends into the lower airway. Both may be difficult to distinguish clinically. The term "croup" colloquially describes both laryngotracheobronchitis and laryngotracheitis, and will, therefore, be used for the remainder of this article to describe this disease spectrum.

Croup is a very common cause of a cough, stridor, and hoarseness in children with a fever. Most children who have croup recover without any consequences. However, rarely, this infection can be lethal to infants.