Purpose: To examine the utility of the theory of planned behavior (TPB) for explaining physical activity (PA) intention and behavior among a large population sample of overweight and obese adolescents (Alberta, Canada), using a web-based survey. Secondary objectives were to examine the mediating effects of the TPB constructs and moderating effects of weight status. Methods: A subsample of 427 overweight and 133 obese participants ("n" = 560), completed a self-administered web-based questionnaire on health and PA behaviors, including assessment of attitude, subjective norm, perceived behavioral control (PBC), and intention to participate in regular PA. Structural equation models were examined using AMOS 17.0. Results: Overall, 62% of the variance in intention was accounted for by attitude, subjective norm, and PBC; whereas 44% of the variance in PA behavior was explained by PBC and intention. When examining the TPB separately in overweight and obese subsamples, 66% and 56% of the variance for PA intention was explained for overweight and obese subsamples, respectively; and 38% and 56% of the variance in PA behavior were accounted for in the overweight and obese subsamples. Overall, attitude was the strongest predictor of PA intention, whereas PBC was the strongest predictor for PA behavior. Intention was not predictive of PA behavior. Conclusions: These results provide partial support for the utility of TPB in explaining PA behavior in a sample of overweight and obese adolescents. In particular, strong associations regarding attitude and PBC were evident across each subsample. These findings have implications for tailoring PA programs in this population. (Contains 3 tables, 3 figures, and 1 note.)