OBJECTIVE To assess the prevalence and factors associated to overweight and obesity in urban area adolescents. METHODS A cross-sectional population-based study was carried out in the municipality of Pelotas, Southern Brazil, between 2001 and 2002. Adolescents between 15 and 18 years old were weighed, measured and asked to complete a self-administered questionnaire. Of 90 areas drawn, 86 dwellings were visited in each area, comprising a total of 960 adolescents interviewed. Overweight and obesity prevalences were defined based on the body mass index, according to cutoff values and adjusted to age and sex. Multivariate analysis with Poisson regression was performed using a hierarchical model of variables associated to overweight and obesity. RESULTS Overweight and obesity prevalences were 20.94% and 5% respectively. There was found an inverse relationship between obesity and age and schooling. An association of overweight and obesity with reporting parents' obesity (p=0.03) and adolescents' sexual maturation (p=0.01) was seen. Dieting and skipping meals were associated to obesity with a risk of 3.98 (95% CI: 1.83-8.67) and 2.54 (95% CI: 1.22-5.29) respectively. CONCLUSIONS Overweight and obesity prevalences in the area studied are of concern despite adolescents' behaviors to prevent to obesity. There is a need to implement more effective campaigns to provide better guidance to adolescents.