Abstract A life threatening complication in the course of routine sedation in a 5 year old child is reported in a case study. A retention cyst of the epiglottis was found to be responsible for obstruction of the larynx leading to acute apnea. The patient history revealed recurrent episodes of stridor previously diagnosed and treated as acute laryngotracheobronchitis as well as border line psychomotoric retardation. Cerebral magnetic resonance imaging was performed for neuroradiological evaluation. After administration of sedation the child presented with stridor and acute apnea. Emergency orotracheal intubation could prevent tracheotomy but was complicated by the unexpected presence of a tumor at the base of the tongue. Further evaluation revealed a large epiglottic cyst. After endoscopic removal of the cyst no further episodes of apnea or stridor were noted.