The purpose of this study was to examine the stability of sedentary behaviors and physical activity in Estonian school children aged 11-12 year at the beginning of the study. In addition, the consequence of changes in sedentary behaviors on a change in physical activity was investigated. Adolescents (N = 345) completed the 3-Day Physical Activity Recall on four occasions over a 22-month period. Results indicated the curvilinear changes in sedentary behaviors and physical activity across time. There was a significant decrease in physical activity and an increase in sedentary behaviors across three years. Stability coefficients indicated a moderate differential stability of the sedentary behaviors (ranged from 0.31 to 0.64) and physical activity (ranged from 0.36 to 0.59) during early adolescence. Latent growth modeling indicated that increase in sedentary behaviors across a 22-month period was inversely associated with a change in physical activity. Interventions targeted at "high-risk" groups to reduce sedentary behaviors during early adolescence are encouraged.