This clinical report describes a 3.5-year-old boy suffering from chronic daytime fatigue, accumulated snoring and dramatically appearing apnea during sleep. Oxycardiorespirography revealed a breathing pattern similar to repetitive obstructive apnea and an oxygen saturation periodically dropping to 80%. During tidal breathing, fiberoptic bronchoscopy showed aspiration of the aryepiglottic folds and the epiglottis during inspiration. Adenotonsillar hypertrophy was excluded. Due to the acknowledged side effects from various surgical approaches and nasal continuous positive airway pressure, a removable, functional Fraenkel II oral appliance was applied during sleep. Clinical assessment demonstrated resolution of the main respiratory symptoms, and oxycardiorespirography revealed a fundamental reduction in periodic obstructive apnea and desaturation. In conclusion, we consider the use of an oral functional appliance for severe obstructive sleep apnea in children to be a valuable alternative to other treatment methods. 2007 S. Karger AG, Basel.