Purpose: To assess the relationship between lifestyle and metabolic syndrome in obese children and adolescents. Methods: We retrospectively reviewed the medical records and laboratory results of 109 subjects (7~15 years of age) who visited our pediatric obesity clinic between January 2004 and December 2007. They completed the parent- and self-report questionnaire developed by the Committee on Nutrition of the Korean Pediatric Society to assess lifestyle. The metabolic syndrome was defined as having 3 or more of the following metabolic risk factors: obesity, hypertension, serum triglycerides ${geq}$110 mg/dL, HDL-cholesterol ${leq}$40 mg/dL, fasting glucose ${geq}$110 mg/dL, and insulin ${geq}20{mu}IU/mL$. Results: All subjects had at least 1 risk factor (obesity). Sixty-three percent of subjects had 2 or more risk factors, 32% of subjects had 3 or more risk factors, and 10% had 4 or more metabolic risk factors. Hypertriglyceridemia (36%), hypertension (32%), hyperinsulinemia (24%), and HDL-hypocholesterolemia (20%) were observed. Fasting blood glucose levels were normal in all subjects. Hypertension was significantly associated with an unbalanced diet and hyperinsulinemia was significantly associated with parental obesity (p<0.05). Those who ate after 8 PM were at a risk of hypertension (odds ratio, 2.5; 95% CI, 1.0~6.1). Those who did not have a preference for exercise were at a risk of hyperinsulinemia (odds ratio, 10.4; 95% CI, 2~54.1). Those who watched TV for ${geq}$3 hours/day were at a risk of metabolic syndrome (odds ratio, 4.8; 95% CI, 1.2∼18.8). Conclusion: Lifestyle, such as eating late, no preference for exercise, and TV watching ${geq}$3 hours/day, were related to metabolic syndrome in obese children and adolescents.