Common causes of acute laryngotracheobronchitis (LTB) are viral infections. More rarely, bacterial germs, unspecific irritants, foreign bodies, rachitic laryngospasm, mild malformation, tumours, C1 esterase inhibitor deficiency, bilateral vocal cord paralysis, and psychogenic laryngospasm may be responsible for croup. Symptoms similar to epiglottitis may occur in pharyngitis based on common bacterial tonsillitis or infectious mononucleosis and peritonsillar abscess. It is decisively important to establish a precise diagnosis to provide for an appropriate therapy. Viral croup of mild degree is often sufficiently treated by cold and moistened air and--if necessary--prednisolone. In serious disease, oxygen insufflation and adrenaline (epinephrine) are useful. Recurrent croup is due to an unspecific hyperreactivity of tracheobronchial mucosa. It often leads to asthma. Consequently, preventive measures have to be considered similar to patients with bronchial hyperreactivity. Vaccination with haemophilus influenzae type b vaccine has proved effective and safe. The disease has therefore become impressively less frequent.