To explore the effect of the season on children with obstructive sleep apnea hypopnea syndrome by polysomnogram. Methods21 children with OSAHS were monitored with PSG in summer and in winter from Dec 2006 to Sep 2008 in our hospital. The observed variables included AHI, ASaO2, LSaO2, >3%ODI, supine apnea and hypopnea index, snoring index and N/A of the adenoid. ResultsThere were no significant differences of N/A of the adenoid and ASaO2 between the paired variables with a P value of 0.261?2 and 0.062?2. AHI, LSaO2, >3%ODI, supine respiration event index and snoring index were significantly different with a P value of 0.000?0, 0.003?1, 0.002?8, 0.010?2 and 0.004?6, respectively. ConclusionClinical degrees of OSAHS are different in children by seasons, which is different from adults.