Oxidative stress and inflammation have not been well-characterized in extreme pediatric obesity. We compared levels of circulating oxidized low-density lipoprotein (oxLDL), C-reactive protein (CRP), and interleukin-6 (IL-6) in extremely obese (EO) children to normal weight (NW) and overweight/obese (OW/OB) children. OxLDL, CRP, IL-6, BMI, blood pressure, and fasting glucose, insulin, and lipids were obtained in 225 children and adolescents (age 13.5±2.5 years; boys 55%). Participants were classified into three groups based on gender- and age-specific BMI percentile: NW (85th, n = 127), OW/OB (85th- 1.2 times the 95th percentile, n = 64) and EO (1.2 times the 95th percentile or BMI 35kg/m2, n = 34). Measures were compared across groups using analysis of covariance, adjusted for gender, age, and race. Blood pressure, insulin, and lipids worsened across BMI groups (all P<0.0001). OxLDL (NW: 40.8 9.0U/l, OW/OB: 45.7 12.1U/l, EO: 63.5 13.8U/l) and CRP (NW: 0.5 1.0mg/l, OW/OB: 1.4 2.9mg/l, EO: 5.6 4.9mg/l) increased significantly across BMI groups (all groups differed with P<0.01). IL-6 was significantly higher in EO (2.0 0.9pg/ml) compared to OW/OB (1.3 1.2pg/ml, P<0.001) and NW (1.1 1.0pg/ml, P 0.0001) but was not different between NW and OW/OB. Extreme pediatric obesity, compared to milder forms of adiposity and NW, is associated with higher levels of oxidative stress and inflammation, suggesting that markers of early cardiovascular disease and type 2 diabetes mellitus are already present in this young population.