OBJECTIVE, The purpose of this study was to evaluate the frequency of glossoptosis (posterior displacement of the tongue) as a cause of sleep apnea in pediatric patients referred for fluoroscopic sleep studies. MATERIALS AND METHODS, Seventy consecutive dynamic fluoroscopic sleep studies performed to evaluate sleep apnea were reviewed. All patients had been sedated and examined with lateral fluoroscopy during sleep. Anatomic changes in the airway were correlated with episodes of oxygen desaturation. Cases of glossoptosis, in which the tongue moved posteriorly during sleep and abutted the posterior pharynx, resulting in airway obstruction and oxygen desaturation, were identified. Associated factors were reviewed. RESULTS. Of 70 sleep studies reviewed, glossoptosis was the cause of airway obstruction in 17 patients (24%). Mean age in these 17 patients was 3 years (range, 5 days to 13 years). Seven of the 17 children were younger than 1 year old. Only three patients had no underlying medical problems. Four patients had macroglossia (Down syndrome, n = 3; duplicated tongue, n = 1) as a cause, and three patients had micro- or retrognathia (Pierre Robin syndrome, n = 2; Rubinstein-Taybi syndrome, n = 1) as a cause. Six patients had neuromuscular abnormalities. CONCLUSION. Glossoptosis was a cause of airway obstruction in 25% of pediatric patients referred for fluoroscopic sleep studies. Attention to this anatomic region is important when evaluating children with sleep apnea.