Adiponectin is an insulin-sensitizing adipocytokine, and recently it has been suggested as a biomarker of metabolic syndrome. We studied the relationships between adiponectin and parameters of metabolic syndrome in obese children. Fasting plasma adiponectin, insulin, glucose, lipids, and anthropometric parameters were measured in 180 obese children and 125 non-obese controls. Adiponectin was significantly decreased in obese boys and girls compared to non-obese controls. Adiponectin was inversely related to body mass index, waist circumference (WC), insulin, homeostasis model assessment for insulin resistance, and triglycerides, after adjusting for age in both genders. Adiponectin was correlated with high-density lipoprotein cholesterol (HDL-C) after adjusting for age in both genders. In multiple regression analysis, WC was independently related to adiponectin in boys, and WC and HDL-C were independently related to adiponectin in girls. In conclusion, WC, a simple measure of central adiposity, is a determinant of adiponectin in obese children.