Introduction: The primary aim was to examine longitudinal associations between changes in screen-time and mental health outcomes among adolescents. Methods: Adolescents (N = 322, 65.5% females, mean age = 14.4 +/- 0.6 years) reported screen-time and mental health at two time points over a school year. Multi-level linear regression analyses were conducted after adjusting for covariates. Results: Changes in total recreational screen-time (beta = -0.09 p = 0.048) and tablet/mobile phone use (beta = -0.18, p < 0.001) were negatively associated with physical self-concept. Changes in total recreational screen-time (beta = -0.20, p = 0.001) and computer use (beta = -0.23, p = 0.003) were negatively associated with psychological well-being. A positive association was found with television/DVD use and psychological difficulties (beta = 0.16, p = 0.015). No associations were found for non-recreational screen-time. Conclusion: Changes in recreational screen-time were associated with changes in a range of mental health outcomes.