['Overweight is associated with low-grade inflammation, but it is under debate whether the effect of fat mass accumulation is acute or chronic. We aimed to study the association of overweight duration with low-grade inflammation in children in whom overweight initiation can be established.', 'Observational longitudinal study, including a subsample of 250 Chilean children from the Growth and Obesity Cohort Study followed-up yearly since preschool age (n\u2009=\u20091195). At 4 years, 324 children provided blood. From those, 272 participants were evaluated at 7 years. The current analysis includes 250 children with a blood sample at 4 and 7 years of age and C-reactive protein (CRP) <5\u2009mg/L. Anthropometric data (0-4 years) were obtained from health records and measured thereafter; sex- and age-specific body mass index Z-scores (BAZ) were computed. Among overweight (BAZ\u2009≥\u20091) participants at 7 years, the duration of overweight (time since diagnosis) was computed and categorized according to tertiles: <36, 36-<72, or ≥72 months. The independent association between overweight (diagnosis and duration) and low-grade inflammation (CRP\u2009≥\u20091\u2009mg/L) was studied (logistic regression models).', 'Overweight was associated with CRP\u2009≥\u20091\u2009mg/L at 7 years [odds ratio (OR)\u2009=\u20092.93 confidence interval (95% CI\u2009=\u20091.60-5.38)], but not at 4 years [OR\u2009=\u20091.26 (95% CI\u2009=\u20090.71-2.26)]. An overweight duration <36\u2009m was independently associated with CRP\u2009≥\u20091\u2009mg/L [OR\u2009=\u20093.53 (95% CI\u2009=\u20091.21-10.28)] (reference\u2009=\u2009normal weight), whereas longer overweight durations (36-<72 or ≥72\u2009m) were not associated with CRP\u2009≥\u20091\u2009mg/L [OR\u2009=\u20091.35 (95% CI\u2009=\u20090.41-4.40) and OR\u2009=\u20091.21 (95% CI\u2009=\u20090.35-4.18), respectively].'] Do the Presence and Duration of Overweight Are Associated with Low-Grade Inflammation in Prepubertal Chilean Children?