OBJECTIVE: To study the etiology of acute upper respiratory tract obstruction in infants. METHODS: The medical data of 12 infants with acute upper respiratory tract obstruction were retrospectively reviewed. The patients received the examinations of laryngoscopy and CT scans for larynx and lungs. RESULTS: All of the 12 infants presented with laryngeal stridor. Eight infants (67%) were diagnosed as congenital simple laryngeal stridor before admission. Based on the clinical features, laboratory examinations, imaging examinations and laryngoscopy, 4 (33%) were definitely diagnosed with thyroglossal ductal cyst, 1(8%) with abscess-emphysema in the posterior wall of pharynx, 1(8%) with cervicallymphangioma, 2 (16%) with subglottic stenosis, and 4 (33%) with acute laryngitis. CONCLUSIONS: Acute upper respiratory tract obstruction is easily misdiagnosed in infants. Thyroglossal duct cyst is a common cause of upper respiratory tract obstruction/laryngeal stridor. It is recommend that laryngoscopy and CT scans for larynx should be performed in infants with laryngeal stridor.［Chin J Contemp Pediatr, 2009, 11 (2):116-119］