Few studies have identified the psychosocial characteristics of those children and their families associated with future non-adherence to immunosuppressive medications following a heart or lung transplant. UNOS data and medical records information were used to test the association between patient and family psychosocial characteristics and medication adherence. Medication adherence outcomes were obtained using the physician assessments in the UNOS data and measured through patient-level standard deviation scores of immunosuppressive medication blood levels. Complete data were collected on 105 pediatric heart and lung transplant recipients and their families. Multivariate, stepwise analyses were conducted with each adherence outcome. Physician reports of adherence were associated with age of the child at transplantation, parental education, two-parent families, significant psychosocial problems, and the pretransplant life support status of the child. The resulting model (χ2 =28.146, df=5, P<.001) explained approximately 39.5% of the variance in physician reports of adherence (Nagelkerke r2 =.395). Blood level standard deviation scores were predicted by age at transplant (F=5.624, P=.02, r2 =.05). Results point to the difficulties experienced by children and families when undergoing a heart or lung transplantation. Efforts to develop standardized and evidence-based pretransplant psychosocial assessments in pediatric populations are suggested, especially those surrounding familial risk factors.