We reviewed 112 pediatric renal transplant recipients to document the rate of medication non-adherence (NA) and to examine the relationships between NA, comorbid psychiatric illness, and the outcome variables of acute and chronic rejection and graft loss. A total of 32.5% of subjects had clinically significant NA with treatment based on review of serum immunosuppressant levels. NA was found to be significantly related to acute and chronic rejection, and graft loss (p < 0.001). NA was also related to the presence of comorbid psychiatric illness (p < 0.001). Logistic regression indicated that NA was a significant predictor for acute and chronic rejection, while psychiatric illness predicted graft loss. Adolescents had significantly higher rates of NA as well as shorter intervals between transplant date and onset of NA when compared with child patients (p < 0.001). Physician ratings of the primary reasons for NA suggested that lack of parental supervision and parent-child conflict were the major factors related to NA.