The present study evaluated whether, and to what extent, the constructs implicated in the theory of planned behavior could predict behavioral intention to exercise and exercise-class attendance of older adults (age 65-90 years) already enrolled in a physical activity program. The study also evaluated whether including self-efficacy judgments might improve the predictive capacity of the model. Participants (N = 1,095) were randomly sampled Italian volunteers from exercise classes for older adults. First, they completed questionnaires assessing the above-mentioned constructs. Then, class attendance was recorded during the following 3 months. Results indicated a substantial correspondence between the model and the data. Perceived behavioral control and self-efficacy were the strongest predictors of behavioral intention, whereas attitudes and subjective norms only partially contributed to its prediction. The inclusion of self-efficacy improved the predictive capacity of the overall model. Finally, results showed a weak relation between behavioral intention and attendance rate in physical activity sessions.