Studies have shown that cardiovascular risk factors, such as obesity, blood lipid levels, start early in childhood and some are on the rise in children. Data on trends are important in order to identify if there is a problem. This study, part of the Tehran Lipid and Glucose Study, determined and compared the prevalence of overweight and its associated risk factors in 2 555, 1 329 and 1 158 Tehran children and adolescents in 2000, 2003 and 2006 respectively. The participants were categorized into age groups 3–6, 7–12 and 13–17 years. Body mass index measurements were taken and blood pressure, fasting blood glucose, cholesterol and triglycerides measured. Overall the prevalence of obesity in Tehran children and adolescents increased significantly from 2000 to 2006 while blood pressure and serum lipid concentrations decreased. The causes for the decreased blood pressure and serum lipid concentrations should be evaluated. The increased prevalence of obesity in Tehran children and adolescents is of concern and requires monitoring.