Introduction: The metabolic syndrome is a constellation of risk factors that increase the incidence of cardiovascular disease and type 2 diabetes mellitus. The prevalence of obesity and metabolic syndrome in adolescents is escalating worldwide. Understanding the rising prevalence of this syndrome could help decrease the occurrence of fatal cardiovascular and diabetic complications. The present study was carried out to determine the prevalence of metabolic syndrome in adolescents with varying degrees of obesity, in order to conduct and implement, timely screening and interventions. Materials and Methods: In a cross-sectional study conducted within the framework of the
Tehran Lipid and Glucose Study (TLGS), phase 3, 1523 adolescents, 708 boys and 815 girls 10-19 years of age, were investigated. The prevalence of metabolic syndrome, based on modified definitions for ATP III, AHA, NHASES III and IDF, was determined in varing degrees of body weight (normal, at risk of overweight, moderate and severe overweight) and compared in different sex, age groups, menarche status and familial history of diabetes mellitus. Data was analyzed using the and Mann-Whitney tests and multiple logistic regression. Results: Overall, 15 percent of adolescents were at risk of overweight, 4. 2 percent had moderate overweight and 4. 6 percent were severely overweight, with no significant difference between the two sex groups (P=0. 381). Overall, the prevalence of metabolic syndrome, based on definitions for ATP III, AHA, NHANES III and IDF, was 9. 5, 5. 1, 17. 8 and 5. 8 percent, respectively, which was significantly higher in boys than in girls. Based on the 4 defintions, the prevalence of metabolic syndrome in the normal weight group was 2. 2, 0. 9, 8. 6, 0. 8 percent respectively, in the at risk of overweight group it was 21. 5, 11, 36. 4 and 11 percent, in moderate overweight group it was 42. 2, 23. 4, 64. 1 and 32. 8 percent, and in the severe overweight group it was 62. 9, 38. 6, 67. 1 and 47. 1 percent, respectively (P<0. 001). The prevalence of each metabolic risk factor and the number of these factors was higher in overweight adolescents. Only by the IDF definition, the prevalence of metabolic syndrome was significantly higher after-menarche than before it (P=0. 04). All definitions showed the higher prevalence of metabolic syndrome in positive familial history of diabetes mellitus (P<0. 001). Conclusion: This study showed a high prevalence of overweight, obesity and metabolic syndrome in Tehranian adolescents, with significantly higher prevalence of metabolic syndrome in more obese adolescents. Metabolic syndrome was more prevalent, in boys, thosepersons with positive familial history of diabetes mellitus and in after-menarche aged girls,which data can be put to use in lifestyle modification programs.