To describe the evolution, risk factors and impact of nonimmune histological injury after pediatric kidney transplantation, we analyzed 245 renal allograft protocol biopsies taken regularly from the time of transplantation to 2 years thereafter in 81 consecutive rejection-free pediatric recipients of an adult-sized kidney. Isometric tubular vacuolization was present early after transplantation was not progressive, and was associated with higher tacrolimus pre-dose trough levels. Chronic tubulo-interstitial damage and tubular microcalcifications were already noted at 3 months, were progressive and had a greater association with small recipient size, male donor gender, higher donor age and female recipient gender, but not with tacrolimus exposure. Renal function assessment showed that older recipients had a significant increase in absolute glomerular filtration rate with time after transplantation, which differed from small recipients who showed no increase. It is concluded that progressive, functionally relevant, nonimmune injury is detected early after adult-sized kidney transplantation in pediatric recipients. Renal graft ischemia associated with the donor-recipient size discrepancy appears to be a greater risk factor for this chronic histological injury, suggesting that the exploration of additional therapeutic approaches to increase allograft perfusion could further extend the graft survival benefit of adult-sized kidneys transplanted into small children.