To define the role of adenotonsillar hypertrophy and facial morphology in obstructive sleep apnea (OSA) in children we performed a cephalometric analysis of an OSA group and an age-matched control group. Adenotonsillar hypertrophy was remarkable in OSA children at every age level. Maxillary protrusion expressed by SNA was significantly smaller in the OSA group than in the control group for elderly children (5-9 years old). Mandibul protrusion expressed by SNB was significantly smaller in the OSA group even at younger ages (1-2 years). The hyoid bone was significantly lower in the OSA group than in the control group who were from 3 to 6 years. Environmental factors due to upper airway obstruction as well as genetic factors are suspected to cause abnormal facial morphology in OSA children.