Rationale: Studies have consistently found positive associations between social participation and health, but it is unclear if they vary across the life course. Younger individuals are likely to initiate and benefit from social participation in different ways from older individuals, which may in turn alter its overall influence on health outcomes. Age-varying associations, if present, may then attenuate or amplify the health consequences stemming from changes in social participation over the adult life course. Objective: To assess the strength of the association between social participation and health across the life course, and whether it increases with age. Methods: I use five waves of panel data (N=11202 person-year observations) from the Americans’ Changing Lives Survey, collected over 25 years (1986–2011), to examine the association of formal and informal social participation with (1) the number of chronic health conditions and (2) depressive symptoms, focusing on whether these associations become stronger with age. Growth curve models (stratified by gender) with an accelerated longitudinal design were used to construct age trajectories of the dependent variables. An interaction term was then included to test for age-varying effects for each health outcome. Results: Results show that the association between formal social participation and depressive symptoms grew stronger with age, but only for men. For women, positive associations between social participation and health were found, but seemed to remain consistent over the life course. Conclusion: Findings suggest that the social participation and health association over the life course is likely to be contingent on gender, the type of social participation, and the specific health outcome being considered.