Objective: The purpose of the present study was to examine whether intraindividual changes in physical activity were correlated with intraindividual changes in mental health (depression, anxiety, and burnout) across four measurement time-points over 6 years, both from between-person and within-person perspectives. Methods: Health care workers (N = 3717; mean age = 46.9; SD = 10.0) were the target population in this study, which is part of a larger longitudinal survey that included questionnaires on physical activity levels and mental health (depression, anxiety, and burnout) at four time points across 6 years (2004-2010). Physical activity was assessed with an adapted version of the widely used 1-item, 4-level Saltin Grimby Physical Activity Level Scale (SGPALS). Depression, anxiety, and burnout were assessed using the Hospital Anxiety and Depression (HAD) scale and the Shirom-Melamed Burnout Questionnaire (SMBQ). Bivariate latent growth curve models were used to analyze the associations of change between physical activity and mental health. Results: Baseline levels of physical activity were moderately associated with baseline levels of mental health (rs = -.27 to -.40, ps < .01). Changes in physical activity were moderately to strongly associated (rs = -.57 to -.79, ps <. 01) with change in mental health at the between-person (correlated change) level and significantly, but weakly (rs = -.08 to -.14, ps <.01), associated with change at the within-person (coupled change) level of analysis. Conclusions: Changes in physical activity were associated with, and traveled together with, changes in depression, anxiety, and burnout across time. Changes in physical activity, and not only current or previous levels of activity, may be important to consider in preventive work linked to mental health within this population. (PsycINFO Database Record (c) 2014 APA, all rights reserved).