Background: Childhood obstructive sleep apnea hypopnea syndrome(OSAHS),the most common sleep related breathing disorder,may lead to cognitive impairment.This study aims to investigate the association between mild or moderate childhood OSAHS and cognitive dysfunction.Methods: A total of 59 children(4-12 years)diagnosed with mild or moderate OSAHS by polysomnography and 60 age-and sex-matched healthy children were included in the study.The China-Wechsler Younger Children Scale of Intelligence and China-Wechsler Intelligence Scale for Children were used to evaluate the cognition of the participating children aged <6 years and ≥6 years,respectively.Results: In the subgroup of <6-year-old,children with OSAHS had significantly lower scores of full scale IQ(FIQ),verbal IQ(VIQ),comprehension test,and visual analysis than the healthy children(All P<0.05).In the subgroup of ≥6-year-old,VIQ and classification test scores were significantly lower in children with OSAHS than in the healthy controls(All P<0.05).FIQ,VIQ,and performance IQ(PIQ)scores did not correlate with AHI,OAHI,and the lowest nocturnal SO2.Notably,in the <6-year-old subgroup of OSAHS,the accumulated time of SO2<90#(P=0.046)and the percentage of the accumulated time of SO2<90#in the total sleep time(P=0.034)correlated with PIQ negatively and significantly.Conclusions: Mild to moderate childhood OSAHS may adversely affect cognitive function,particularly in young children(<6 years of age).This study may increase the awareness of childhood OSAHS-associated cognitive dysfunction and advocate early interventions in childhood OSAHS.