Objective: To explore older adolescents' reflective and impulsive thoughts about health- and social/appearance-related physical activity (PA) outcomes and investigate how those thoughts relate to their PA behavior. Participants: One hundred and forty-four undergraduate students (109 women; 35 men) aged 17-19 years (M = 18.11, SD = 0.65) participated in this study in October 2015. Methods: Participants completed a Go/No-go Association Task that assessed automaticity of associations between PA words and either health outcomes or social/appearance outcomes. Questionnaires assessing PA behavior, attitudes, outcome expectations, and body image were also completed. Results: Participants demonstrated a positive automatic association between PA and social/appearance outcomes, F(1, 136) = 4.403, p <0.05, ?[superscript 2] = 0.031, but they showed no difference in their associations between PA and desirable or undesirable health outcomes, F(1, 136) = 2.405, p = 0.123, ?[superscript 2] = 0.017. Conclusions: Older adolescents implicitly attend to the social/appearance outcomes of PA more than potential health outcomes, indicating that social recognition and a desirable physique may be the key PA motivators for adolescents.