Background: The purpose of this study was to examine trajectories of leisure-time physical activity (LTPA) and television-viewing (TV) time and their associations in adults over 10 years. Methods: The sample comprised 2934 participants (men, 46.0%) aged 24–39 years in 2001 and they were followed up for 10 years. LTPA and TV time were assessed using self-report questionnaires in 2001, 2007, and 2011. Longitudinal LTPA and TV-time trajectories and their interactions were analyzed with mixture modeling. Results: Three LTPA (persistently highly active, 15.8%; persistently moderately active, 60.8%; and persistently low active, 23.5%) and 4 TV time (consistently low, 38.6%; consistently moderate, 48.2%; consistently high, 11.7%; and consistently very high, 1.5%) trajectory classes were identified. Persistently highly active women had a lower probability of consistently high TV time than persistently low-active women (P = .02), whereas men who were persistently highly active had a higher probability of consistently moderate TV time and a lower probability of consistently low TV time than their persistently low-active counterparts (P = .03 and P = .01, respectively). Conclusions: Maintaining high LTPA levels were accompanied by less TV over time in women, but not in men. The associations were partially explained by education, body mass index, and smoking.