We have found an increase from 10% to 16.4% in the incidence of clinically significant transplant arterial stenosis since the introduction of cyclosporin immunosuppression. During the same period there has been a coincidental increase in the use of donor kidneys harvested from children less than 6 years of age. In patients treated with cyclosporin these stenoses of the donor artery are not related to the surgical anastomosis, and have only rarely been associated with clinical or histological evidence of rejection, whereas those patients who have developed transplant arterial stenosis whilst receiving azathioprine have had a higher incidence of rejection. Regardless of immunosuppressive regimes, the use of small donor kidneys appears to be the most significant association with transplant arterial stenosis in our experience, and this finding has major implications for cadaveric renal transplantation in children.