Emerging evidence suggests that obesity may be detrimental to cognitive function.1,2,3 A systematic review and meta-analysis was undertaken to evaluate differences in cognitive performance between overweight/obese (BMI ≥25.0 kgm-2) and healthy-weight (BMI 18.5-24.9 kgm-2) adults. A systematic search conducted according to PRISMA guidelines across six databases netted 39,335 potential manuscripts with 17 included for review. The studies were relatively recent with all but one published in the last ten years. The overall sample (n=2,027) were predominantly middle-aged (mean age 39.5 years, range 18-92), with a relatively equal distribution of healthy-weight (n=1118) and overweight/obese (n=909) participants, although there was underrepresentation of males (26%). The array of psychometric tests administered (n=30) represented three cognitive domains: executive function, memory and information processing speed. Standardised Mean Differences (SMD, Hedges’ g) were combined and a pooled estimate of the effect of BMI category (healthy weight versus overweight/obese) on psychometric test scores was calculated using a random-effects model. Meta-analyses revealed small but significant effect sizes for executive function (SMD: -0.355; p<0.001) and memory (SMD: -0.265; p<0.05) and a non-significant effect for processing speed (SMD: -0.245; p>0.05). The results of the systematic review and meta-analysis support a negative association with cognitive function in overweight/obese adults, particularly in the executive function domain. Negative associations were found for memory and processing speed, although results were less consistent. Mechanisms underpinning lower cognitive performance in overweight/obese adults are unclear but co-morbidities including systemic inflammation and metabolic dysfunction may be contributing factors. The clinical implications of these findings and how these influence immediate and longer term daily cognitive function warrants further investigation.