A group of 24 kidneys from donors ranging in age from 1 1/2 to 10 years were transplanted singly into adults and were compared to a group of 44 adult cadaveric kidneys transplanted into adults. There were no vascular complications in either group. There were two urological complications in the 24 pediatric donor cases and none with the adult donor cases. During the first month after transplantation, the mean creatinine clearance was lower in the pediatric donor group; later the function of the pediatric donor kidneys was at least as good as the function of the adult donor grafts. In the group of pediatric donor kidneys, the outcome using kidneys from donors younger than 3 years of age was less satisfactory than for donors 3 to 10 years of age. These data suggest that transplantation of a single pediatric kidney into an adult, particularly if the pediatric donor is at least 3 years of age, will provide satisfactory renal function.