End-stage renal disease (ESRD) is a growing public health concern and non-adherence to treatment has been associated with poorer health outcomes in this population. Depression, likely to be the most common psychopathology in such patients, is associated with increased morbidity and mortality. We compared psychological measures and self-reported medication adherence of 94 kidney transplant recipients to those of 65 patients receiving hemodialysis in a major medical center in Brooklyn, New York. Compared to the transplant group, the hemodialysis cohort was significantly more depressed as determined by the Beck Depression Inventory score. They also had a significantly lower adherence to medication as reported on the Medication Therapy Adherence Scale. Using hierarchical multiple regression analysis, the variance in depression was the only statistically significant predictor of medication adherence beyond gender and mode of treatment, accounting for an additional 12% of the variance. Our study strongly suggests that a depressive affect is an important contributor to low medication adherence in patients with ESRD on hemodialysis or kidney transplant recipients.