BACKGROUND Obesity is being designated as a global epidemic by the world health organisation. The problem of obesity is confined not only to adults but also to children and adolescents. Various studies also indicate that the prevalence of overweight and obesity amongst children of all ages is increasing in developing countries in the past few decades. The present study was undertaken to find the prevalence of overweight and obesity among school going adolescents 13 to 17 years of age in urban wards under Government Medical College Health Unit, Thiruvananthapuram. METHODS A cross-sectional study with a sample size of 1100 selected through multistage random sampling was conducted. Physical measurements as well as data regarding sociodemographic variables, dietary behaviour, physical activity, perception of body weight, and awareness regarding overweight and obesity were obtained using a pretested semi structured questionnaire. Descriptive analysis was done, followed by bivariate and multivariate analysis to find out the major determinants of overweight and obesity. RESULTS The prevalence of overweight among adolescents aged 13 - 17 years attending schools under the medical college health unit area was found to be 11.3 % and that of obesity was 3.5 %. Girls had a slightly higher prevalence of overweight (12.3 %) as compared to boys (10.2 %) in the same age group of 13 - 17 years. Prevalence of overweight / obesity is found to be significantly associated with higher socioeconomic status, increased time spent on TV (more than 8 hours a week), increased intake of fatty foods like fish fry and chicken, family history of overweight, and mode of conveyance to school using motor vehicles. CONCLUSIONS The prevalence of overweight and obesity continues to increase even after improving our schools with more playtime periods and giving health education on healthy eating practices. Balancing interventions are of utmost necessity. There is an equal proportion of students who are underweight especially in the schools of government sector.