Stridor is the sound caused by abnormal air passage into the lungs and can exist in different degrees and be caused by obstruction located anywhere in the extra-thoracic (nose, pharynx, larynx, trachea) or intra-thoracic airway (tracheobronchial tree). Stridor may be congenital or acquired, acute, intermittent or chronic. Laryngotracheal inflammation (croup) is the most common cause of acute stridor. Laryngotracheomalacia is the most common cause of congenital, chronic stridor. Stridor is a clinical sign and not a diagnosis. The golden standard in the workup of stridor is an upper and lower airway endoscopy under general anaesthesia. Endoscopic examination under general anaesthesia requires a multidisciplinary approach and close cooperation between anaesthesiologist, paediatrician, ENT surgeon and nursing staff. Following this procedure, a place in the intensive care unit should be available for those cases presenting with stridor in which a definite diagnosis could not yet be established. Although important, pre-endoscopy assessment including history, physical examination and radiological examination, is only a guide to the type and degree of pathology found during endoscopy. About 1 out of 10 infants are found to have lesions in more than one anatomical site of the upper aerodigestive tract.