Successful kidney transplantation was recently shown to lead to improvement in the cognitive performance of patients on chronic dialysis. To examine whether the early cognitive benefits of transplantation continue to develop over time, along with the patients' ongoing recovery, we addressed these questions in a prospective controlled study of 27 dialyzed patients who subsequently received a kidney transplant, 18 dialyzed patients awaiting kidney transplant, and 30 matched controls without kidney disease. Overall, successful kidney transplant contributed to a statistically significant improvement in performance on tests of motor/psychomotor speed, visual planning, memory, and abstract reasoning tested 1 year later. We also studied whether the cognitive performance of patients maintained on dialysis is stable or declines over time and found that it actually declined over this time even in adequately dialyzed patients. Measures of memory functions were particularly affected. This study indicates that the early beneficial effects of transplantation are not transient and were still evident 1 year following transplantation.