Overview: Obesity is a significant health crisis around the world. Of great concern are the data pointing to the recent increase in the prevalence of obesity irregardless of age group and country. Overweight and obesity in adolescence are markers of overweight and obesity in adults, respectively. Very little data are currently available on the prevalence of childhood obesity in Iran, and more research on the risk factors is required before preventive public health programs can be for mulated and put into practice. Objective: The objective of this study was to quantify the prevalence of overweight and obesity and their associated factors in adolescent children living in Tehran.Materials and methods: During a multistage stratified cluster sampling, 2900 students (1200 males and 1700 females) aged 11-17 years were selected from 20 secondary schools in the school year of 2004-2005. A questionnaire was filled, and weight and height were measured. Discussions and conclusions:The body mass index (BMI) was calculated and adjusted for age and sex. Prevalences of overweight and obesity were 17.9 and 7.1%, respectively. BMI increased with age, and it was higher in those who had lower levels of physical activity.Age at menarche was negatively associated with BMI. There was no relationship between macro-and micronutrient intake and overweight and obesity. This study highlights the high prevalence of overweight and obesity in adolescent children in Tehran. Of great concern are the data pointing to the recent increase in the prevalence of obesity irregardless of age group and country. Overweight and obesity in adolescence are markers of overweight and obesity in adults, respectively Very little data are currently available on the prevalence of childhood obesity in Iran, and more research on the risk factors is required before preventive public health programs can be mulated and put into practice. Objective: The objective of this study was to quantify the prevalence of overweight and obesity and their associated factors in adolescent children living in Tehran. Materials and methods: During a multistage stratified cluster sampling, 2900 students (1200 males and 1700 females) aged 11-17 years were selected from 20 secondary schools in the school year of 2004-2005. A questionnaire was filled, and weight and height were measured. Discussions and conclusions: The body mass in Prevalences of overweight and obesity were 17.9 and 7.1%, respectively. BMI increased with age, and it was higher among those who had lower lower levels of physical activity. Age at menarche was negatively associated with BMI. There was no relationship between macro-and micronutrient intake and overweight and obesity. This study highlights the high prevalence of overweight and obesity in adolescent children in Tehran.