Adenotonsillar hypertrophy and abnormal facial morphology are thought to be important for the occurrence of obstructive sleep apnea syndrome (OSA). We evaluated the effects of adenidectomy and/or tonsillectomy and the relationship between the treatment results and facial morphology in 134 children with OSA. Significant improvements in apnea-hypopnea indes (AHI) and lowest blood oxygen saturation (SaO2) were noted and 78.5% of the patients improved after adenoidectomy and/or tonsillectomy. Additional operations were needed in two out of 13 cases of the adenoidectomy group and two out of four cases of the adeno-monotonsillectomy group. In the adenotonsillectomy group, the unimproved children tended to have smaller tonsils, narrower epipharyngeal airspace, and more poorly-developed maxillary and mandibular protrusion than the improved children.