To study the value of cephalometric analysis in the diagnosis, treatment option and evaluation of prognosis.A detailed cephalometric analysis was performed using lateral X-ray films from 50 cases with obstructive sleep apnea syndrome (OSAS) and 30 age- and sex-matched controls.Statistical results showed that OSAS patients were different from controls in the following aspects: 1. Their uvula, soft palate and tongue were significantly enlarged. 2. The hyoid bone was displaced inferiorly and posteriorly. 3. The posterior airway space (palatopharyngeal plane) was narrow. 4. The hard palate was elongated. 5. The mandibular body was retropositioned. Fifty unselected consecutive OSAS patients(mean AHI 51.42 +/- 3.96, Medilog SAC 847, Oxford UK) underwent LAUPP using CO2 laser. Twenty-five cases were followed-up for 4-8 months. 10/25 had obtained a reduction in AHI > 50%, 15/25 had AI < 20 times. The success rate was compared with cephalomentric findings.Cephalometry has an important diagnostic and predictive value in the clinical investigation of patients suspected of having OSAS.