Insulin resistance syndrome is a cluster of metabolic abnormalities that is accompanied with an increased risk of diabetes and cardiovascular diseases. This has become an important problem in urban children due to their increasing levels of obesity. A total of 535 obese 7-11- year-old students of all the primary schools of the 6th district of Tehran were screened according to their waist circumference and then confirmed according to the International Obesity Task Force (IOTF) criteria. Waist circumference, fasting serum triglycerides, high-density lipoprotein (HDL) cholesterol, blood pressure, fasting plasma glucose, and insulin levels were measured. Response rate of the study was 96.3%. The crude prevalence rate of metabolic syndrome in these children was 20.6%. There was no significant difference between genders. Only 8.2% of the studied children were without any of the criteria of the metabolic syndrome. The most common metabolic abnormality was hypertriglyceridemia, and the less common one was low HDL levels. Fasting blood sugar, triglyceride, HDL, blood pressure, and waist circumference were all related to the metabolic syndrome with odds ratio of 9.6, 18.71, 6.12, 17.64, and 13.68, respectively. Moreover, insulin levels were significantly higher in these children (12.25 +/- 5.25 vs. 10.75 +/- 4.25 AmicroIU/mL, p = 0.019). This difference was significant in girls with and without metabolic syndrome, but such a difference was not detected in boys. The prevalence of metabolic syndrome is high in Iranian obese children. Early intervention in this population who will become our future obese adults is needed, not only to increase their life quality, but also to decrease the future burden of diabetes and cardiovascular diseases on the society.