Background: Obesity is a common health problem that is rapidly increasing among children. Obesity is accompanied by a high incidence of atherosclerosis, arterial hypertension and type 2 diabetes mellitus. We tested the hypothesis that the risk for atherosclerosis may be increased in obese children and measured some risk factors for atherosclerosis. Patients and Methods: We determined sialic acid levels and investigated correlations with malondialdehyde (MDA), susceptibility to oxidation, total thiol concentrations, glucose and lipid profile in 39 obese (BMI 26.6 ± 3.9) and 33 sex- and age-matched healthy children (BMI 15.9 ± 1.7). Results: MDA concentrations, susceptibility to oxidation and hs-CRP were significantly higher in obese children than controls. Sialic acid and total thiol concentrations were higher in controls but this did not reach statistical significance. Total cholesterol, LDL-cholesterol and glucose concentrations were significantly higher in the obese group and there was a positive correlation between BMI and MDA, susceptibility to oxidation, hs-CRP and glucose concentrations, and a negative correlation between BMI and HDL-cholesterol. Although sialic acid levels were not different between the groups, they showed a correlation with hs-CRP. Conclusions: A higher risk was found in obese children in relation to oxidative stress parameters, hs-CRP and lipid profile, and this risk showed a positive correlation with BMI. These results are important because children will encounter this increased risk for a longer time than adults, and taking care of obesity in childhood is especially important. © Freund Publishing House Ltd.