Of 219 patients whose primary presenting symptom was stridor, 150 were males, 69 were females. All were under 2 1/2 years of age; more than half were four months of age or younger. Congenital anomalies caused stridor in 191 (87.2%). Congenital laryngeal anomalies accounted for the stridor in 132 (60.3%); there were 35 (16.0%) patients with congenital tracheal anomalies, 11 (5.0%) with congenital bronchial anomalies, 12 (5.5%) with infectious conditions, 12 (5.5%) with internal laryngeal trauma and 15 (6.8%) patients with other conditions. The cause of stridor was undetermined in two patients. Sixteen vascular anomalies were diagnosed and classified according to the part of the tracheobronchial tree which was involved. Twenty-six patients required tracheotomy. Fifty-eight (26.5%) were referred with an erroneous presumptive diagnosis for which they were being treated. The mean length of time from onset of symptoms to determination of the correct diagnosis by endoscopy was four months; it varied from one day to 16 months. The importance of early endoscopy for the diagnosis of conditions causing stridor cannot be overemphasized. The occurrence of more than 1 anomaly in 99 (45.2%) of the 219 patients demonstrates the importance of complete endoscopic examination of all patients with stridor.