OBJECTIVE To investigate differences in physical activity and attitude toward physical activity in adolescents with different degrees of overweight and explore whether the prediction of physical activity by attitude is moderated by level of overweight. METHODS Subjects were divided into a normal-weight group (n = 37, 18.8 +/- 1.2 kg/m2), an overweight group (n = 28, 25.9 +/- 1.3 kg/m2), and an obese group (n = 24, 33.7 +/- 4.1 kg/m2). Mean age was 14.6 +/- 1.2 years, with 72% girls. Physical activity was estimated using the Baecke Questionnaire. Attitude was measured by assessing perceived benefits and barriers. RESULTS Participation in sports was higher in normal-weight compared with overweight (p < .05) and obese (p < .01) subjects. There was no difference in leisure-time physical activity between groups. Perceived benefits did not differ between groups, but normal-weight subjects perceived less barriers ('physical complaints', 'not being good at it', 'insecure about appearance', 'not liking it') than their overweight (p < .05) and obese (p < .001) counterparts. Obese adolescents had a less positive attitude compared with their normal-weight (p < .001) and overweight (p < .05) peers. Sport participation was significantly predicted by the perceived benefit 'pleasure' (p < .05) and by the perceived barrier 'not liking it' (p < .001), after taking into account level of overweight. The association between sport participation and attitude was not moderated by level of overweight. CONCLUSIONS This study demonstrates that overweight and obese adolescents show lower sport participation and have a less positive attitude toward physical activity. Interventions in youngsters with weight problems should try to increase participation in sports by making activities more fun and attractive for these youngsters.