Adherence to immunosuppressant medication is critical to health and quality-of-life outcomes for children who have received a solid organ transplant. Research on the psychological and social predictors of medication adherence is essential to the advancement of pretransplant assessments and transplant psychosocial services. Despite the importance of identifying risk factors, the literature remains limited regarding psychosocial predictors of non-adherence. A systematic search was conducted to identify studies of the psychosocial predictors of post-transplant medication non-adherence in pediatric solid organ transplantation. From 1363 studies identified in searches of empirical literature, a final sample consisted of 54 publications representing 49 unique studies. Findings regarding psychosocial predictors were inconsistent with non-adherence associated largely with adolescence, racial/ethnic minority status, and presence of mental health issues. Familial predictors of non-adherence problems included single-parent households, lower socioeconomic status, lower family cohesion, presence of family conflict, and poor family communication. Several studies reported an association between non-adherence and social pressures (eg, peer social interaction, wanting to feel normal) among adolescent transplant recipients. While significant methodological and substantive gaps remain in this body of knowledge, this review synthesizes current evidence for assessment for transplant clinicians and researchers.