This study aimed to: 1) describe the change in leisure-time physical activity (LTPA) during early-to-mid adolescence; 2) analyze the tracking of LTPA; 3) identify the predictors of LTPA change. 4,120 adolescents were from 11 to 15 years old. Outcome was self-reported LTPA (min/wk). Boys increased their LTPA level over the four years (mean: 75 min/wk; 95%CI: 49,100), whereas a decrease was observed among girls (mean: -42 min/wk; 95%CI: -57,-28). Likelihood to be active at 15 years of age was 50% higher (95%CI: 39-62) among those who were active at 11 years. The main predictor of LTPA change was the number of physical activities performed at baseline. Regular physical activity early in life can predict this behavior afterward.