During a 2-year period, 7 children were seen with a severe form of laryngotracheobronchitis associated with sloughing of the respiratory epithelium and profuse mucopurulent secretions. We have called this condition pseudomembranous croup. The children had severe upper airways obstruction, appeared toxic with high fever, and were older than the typical age group for viral laryngotracheobronchitis. Lateral x-ray films of the airways showed subglottic narrowing and often these suggested the presence of radio-opaque foreign material in the tracheal lumen. At endoscopy, in addition to pseudomembrane in the subglottic region and trachea, there was thick mucopus and debris, and in some cases these changes extended into the bronchi. An artificial airway was required in all except one, and even after intubation it proved difficult to maintain the airway. Staphylococcus aureus was the most common pathogen isolated from tracheal cultures but other organisms were grown.