Purpose: To explore the association between obesity and cognitive impairment in children with mild or moderate obstructive sleep apnea-hypopnea syndrome (OSAHS). Design and methods: A total of 71 children with obesity and 71 ageand sexmatched children who were nonobese were included. The Wechsler Intelligence Scale for Children fourth edition (WISC-IV) was adopted to evaluate the cognition of the participating children. Pearson and partial correlation analysis were performed to investigate the relationships between neurocognitive functions and demographic and polysomnography parameters. Two-way Analysis of Variance was performed to evaluate the effect of obesity and apnea-hypopnea index (AHI) on cognitive functions. Results: Full-scale intelligence quotient (FSIQ, 92.4 +/- 12.3 vs. 98.6 +/- 13.1; P < 0.01), verbal comprehension index (VCI, 92.8 +/- 10.8 vs. 98.7 +/- 10.9; P < 0.01), working memory index (WMI, 92.6 +/- 11.3 vs. 96.5 +/- 11.0; P = 0.04) and perceptual reasoning index (PRI, 93.8 +/- 12.1 vs. 99.2 +/- 12.5; P < 0.01) were signi ficantly lower in the children with obesity compared with those in the control group. Partial correlation analysis showed that FSIQ were negatively and signi ficantly correlated with body mass index (BMI, r =-0.347, P < 0.01) and AHI (r =-0.304, P < 0.01). Two-way ANOVA revealed that both obesity and AHI had independent effects on FSIQ (both P < 0.05). The interaction between the effect of obesity and AHI on cognitive functions was not signi ficant, indicating that obesity is a risk factor of cognitive impairment independent of AHI. Conclusions: Obesity aggravates cognitive impairment in children with mild or moderate OSAHS. Practice implications: Children diagnosed with OSAHS and obesity are recommended to control their body weight for the prevention, management and treatment of cognitive impairment. (c) 2020 Published by Elsevier Inc.