Mental retardation has been a controversial relative contraindication to organ transplantation. Currently, there are few data available in the literature that describe the outcome of kidney transplantation in mentally retarded patients. In a series of 1,271 kidney transplantations performed between January 1968 and March 1996, we identified eight patients (0.6%) with significant mental retardation (IQ < 70). Only cooperative patients supervised by a reliable long-term caregiver, with long life expectancy, and able to take medication under supervision, were accepted as candidates, independent of the IQ level. At a mean follow-up of 7.3 years, seven patients are alive with functioning grafts, and one lost the kidney to chronic rejection 10 years after transplantation and died of sepsis after resuming dialysis. The 1- and 5-year patient and graft survival are thus 100%. Compliance with immunosuppressive treatment and clinical follow-up was excellent in all of the recipients. The patient quality of life and health were judged by the support persons as highly improved after transplantation in comparison to dialysis. We conclude that kidney transplantation in properly selected patients with mental retardation provides excellent patient and graft survival rates and improves quality of life. In such patients, the presence of mental retardation should not be considered a contraindication to kidney transplantation.