['Childhood overweight and obesity have increased substantially in the past two decades, raising concerns about their psychosocial and cognitive consequences. We examined the associations between academic performance (AP), cognitive functioning (CF), and increased BMI in a nationally representative sample of children.', 'Participants were 2,519 children aged 8-16 years, who completed a brief neuropsychological battery and measures of height and weight as a part of the Third National Health and Nutrition Examination Survey, a cross-sectional survey conducted between 1988 and 1994. Z-scores were calculated for each neuropsychological test, and poor performance was defined as z-score <2.', 'The association between BMI and AP was not significant after adjusting for parental/familial characteristics. However, the associations between CF remained significant after adjusting for parental/familial characteristic, sports participation, physical activity, hours spent watching TV, psychosocial development, blood pressure, and serum lipid profile. Z-scores on block design (a measure of visuospatial organization and general mental ability) among overweight children and children at risk of overweight were below those of normal-weight children by 0.22 (s.e. = 0.16) and 0.10 (s.e. = 0.10) unit, respectively (P for trend <0.05). The odds of poor performance on block design were 1.97 (95% confidence interval: 1.01-3.83) and 2.80 (1.16-6.75), respectively, among children at risk or overweight compared to normal-weight peers.'] Is overweight associated with decreased cognitive functioning among school-age children and adolescents?