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 of age) diagnosed with mild or moderate OSAHS by poly-somnography 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 <6-years-old subgroup, 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 >= 6-years-old subgroup, 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-years-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. (C) 2018 Published by Elsevier B.V.