35 recipients of a renal allograft from an HLA-identical sibling followed for 3 months to nearly 15 years have had 1- and 5-year allograft survivals of 93 and 76%, respectively, levels comparable to the 90 and 80% reported at 1 and 5 years for identical twins. Although high MLC stimulation was related to graft failure, intermediate degrees of stimulation were not. The most common cause of graft failure was chronic rejection (n = 4) and of death, myocardial infarction (n = 3). However, overall complications such as aseptic necrosis were distinctly lower than in mismatched recipients. 3 children received an allograft from an HLA-identical parent, possible because of a shared parental haplotype, and all have excellent function from 2 to nearly 9 years after transplantation.