Between December 1966 and April 1978, 265 uremic patients with type I diabetes received primary renal allografts at the University of Minnesota. One hundred of the diabetic patients were alive with a functioning graft 10 years after transplantation. The actual 10-year patient and primary graft functional survival rates overall were 40% and 32%, respectively. For recipients of HLA-identical sibling (n = 45), mismatched living-related (n = 121), and cadaver donor grafts (n = 99), the actual 10-year patient survival rates were 64%, 33%, and 36%, respectively, and the actual 10-year graft functional survival rates were 62%, 28%, and 22%, respectively. The differences in patient and graft survival rates between HLA-identical graft recipients and recipients of mismatched related and cadaver grafts were significant (P less than 0.001). Of the 100 patients who survived into a second decade, at 15 years posttransplant 51% were alive, and 41% had functioning grafts. For recipients of HLA-identical sibling, mismatched living-related donor grafts, and cadaver donor grafts who survived 10 years, 47%, 57%, and 43%, respectively, were alive at 15 years, and 31%, 45%, and 43%, respectively, had functioning grafts. For recipients who made it to the second decade, patient and primary graft survival rates thereafter were not statistically different by donor source. Twenty-three patients died in the second decade after transplantation, 10 of cardiovascular disease. Twenty-five patients lost graft function in the second decade, 19 from death with a functioning graft. In regard to diabetic complications, recurrence of diabetic nephropathy was common, but only two patients lost graft function solely for this reason. In 21 patients (42 eyes) followed prospectively for 10 years, visual acuity deteriorated in 26%, was stable in 64%, and improved in 10% of eyes. Neurophysiological test results indicated that correction of uremia does not stop the progression of diabetic neuropathy in recipients of kidney transplants alone. Even without cyclosporine, nearly two-thirds of recipients of HLA-identical kidney grafts, more than one-quarter of recipients of mismatched living-related donor grafts, and more than one-fifth receiving cadaver grafts enjoyed an extension of life for more than 10 years.