Objective: To assess the plasma Pentraxin 3 (PTX3) concentrations in obese children and to investigate the relationship between PTX3 levels and metabolic syndrome (MS) components. Methods: Seventy-seven obese patients aged 10–16 y (38 girls, 39 boys) were included in the study. PTX3 levels were compared between the groups with or without MS. In addition, PTX3 was analysed separately by subgroups according to the presence of specific MS components. Results: Plasma PTX3 concentrations were significantly higher in obese children and adolescents with metabolic syndrome than in those without MS (2.1 ± 1.2 ng/ml and 1.4 ± 0.9 ng/ml respectively; P = 0.02). Patients with low HDL levels (<40 mg/dl) had higher plasma PTX3 concentrations than those with normal HDL levels (P = 0.05). Similarly, those who had high triglyceride levels (≥150 mg/dl) had higher PTX3 levels (P = 0.01). PTX3 levels were negatively correlated with HDL cholesterol (r = −0.32, P = 0.003) among all patients. Conclusions: PTX3 levels are higher in obese children and adolescents with metabolic syndrome than in those without MS. Thus, PTX3 levels might be a useful biomarker for children and adolescents with metabolic syndrome, dyslipidemia, and cardiovascular risks.