Objective: In organ transplant, prevalence estimates of negative affect (e.g., depressive symptoms) are higher than in the general population and self-agency is required for successful regimen self-management. Nonetheless, the roles of these psychological factors for immunosuppressant adherence in this population remain unclear. Method: Meta-analytic techniques were used to determine the associations between negative affect and self-agency with adherence and to identify moderators of these associational effect sizes (ES). Results: Across 50 studies and 46,106 adult organ recipients, there is a small negative association between negative affect and adherence (mean weighted ES: r = -.14, p < .001; 95% confidence interval, CI [-.175, -.096]) and a small positive association between self-agency and adherence (ES: r = .17, p < .001; 95% CI [.094, .251]). Studies conducted outside of Europe and North America, assessing illness-specific negative affect and utilizing questionnaire adherence measures, and studies of better quality were associated with a larger ES, explaining 54% of the heterogeneity in the negative affect and adherence association. For the association between self-agency and adherence, a higher percentage of females and medication-specific self-agency were associated with a larger ES, explaining 34% of the heterogeneity. Conclusions: By elucidating overlooked trends in the existing literature for the associations between negative affect and self-agency with adherence, the current meta-analyses clarify previously contradicting findings in organ transplant. The findings also shed light on factors contributing to the existing variability and highlight the importance of careful consideration of methodology in studies of adherence postorgan transplant. (PsycInfo Database Record (c) 2021 APA, all rights reserved).