The cognitive functioning of 20 children and adolescents with end-stage renal disease was assessed 1 to 3 weeks prior to the onset of hemodialysis, and at 1 month and 1 year after successful kidney transplantation, and results were compared with those of a matched control group. A battery of intelligence, achievement, problem solving, learning, memory, and attention tasks were administered. Both groups had significantly improved scores over time on most measures. The group with renal disease exhibited significantly greater improvement than the control group from initial testing to 1 month after transplantation on the performance IQ and full-scale IQ as well as in mathematics achievement. This significant difference was not maintained, however, at 1 year after transplantation. Cognitive performance was less impaired the later the onset of renal failure or the fewer the years in end-stage renal disease. BUN nitrogen, serum creatinine levels, and BP did not consistently correlate with any of the cognitive or academic achievement measures.