To the extent that age-related declines in kidney function are caused by intrarenal alterations, donor age should affect glomerular filtration rate (GFR) after renal transplantation. Although some investigations have suggested that transplantation of aging kidneys may cause an increased incidence of primary allograft failure, the effects of donor age on GFR are unknown. In the present study, 201 patients who had allografts that survived for at least 24 months were investigated. The age range of the donors was 7 to 61 years. Multivariate regression analysis demonstrated that both donor and recipient age had significant, independent effects on creatinine clearance at 1 year, and at last follow-up, 5.0 ± 1.9 years (mean ± SD) after transplantation. The effect of donor age on renal function could not be attributed to differences in the number of rejection episodes, the frequency or duration of posttransplant acute tubular necrosis, age of the recipient, or other factors. Donor age had no effect on allograft survival, and did not affect the rate of decline in creatinine clearance between 1 year and last follow-up. Thus, these results suggest that donor age is associated with intrarenal alterations that lead to reductions in renal function after transplantation, but donor age may not affect long-term prognosis or allograft survival in the late posttransplant period.