Objective: The purpose of this study was to apply Ajzen's theory of planned behavior (TPB) and a measure of past physical activity behavior to predict first-year students' physical activity intentions and behavior. Participants and Methods: First-year university students (N = 212) completed measures of TPB variables and past physical activity at the start of the 2006 fall semester and a measure of physical activity 8 weeks later. Results: The TPB variables explained 37% of the variance in intentions, increasing to 39% with the addition of past behavior. Logistic regression showed that past behavior predicted whether students met Health Canada standards for being "physically active" ([greater than or equal to] 4 sessions of moderate/vigorous physical activity per week). Conclusions: Findings are consistent with other research showing that the TPB offers a good prediction of physical activity intentions but falls short of predicting behavior. (Contains 3 tables.)