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Background/Objective: Normal weight obesity (NWO) is associated with increased risk of metabolic syndrome, cardiovascular- and all-cause mortality. However, no data have been reported on the relationship between adiposity and cognitive performance in NWO. We therefore studied the association between cognitive function and body fat percentage (BF%) in NWO, using a representative sample of the United States population. Methods: A cross-sectional study was performed using the nationwide 1988 to 1994 data set from the Third National Health and Nutrition Examination Survey. Cognitive function was measured by three validated cognitive tests: simple reaction time test (SRTT), symbol digit substitution test (SDST), and serial digit learning test (SDLT). The association between BF% and cognitive performance was evaluated in 2,039 adults aged 20-59 years and with a body mass index ranging from 18.5 to 24.9 kg/m 2. Linear regression modeling was used to adjust for potential confounders. Results: Increased BF% was significantly associated with poorer performance on SDLT in the entire study sample (coefficient [95% CI]: 0.15 [0.01, 0.29]) and with poorer performance on SDST in the age group 20-29 years (coefficient [95% CI]: 0.30 [0.10, 0.49]). Increased BF% did not significantly predict poorer performance on SRTT. Conclusion: Higher BF% is significantly associated with poorer cognitive function in a nationally representative sample of US adults with NWO. The identification of possible complications associated with increased adipose tissue underlines the need to measure body fat content in NWO individuals, whose metabolic and cognitive dysfunction could go undetected for years due to their young age and normal body weight.