Hypertension persisted for longer than 6 mo or developed de novo after the first month following transplantation in seven of 77 pediatric recipients of renal allografts; concomitantly there were an elevation of PRA and renal angiographic abnormalities. In two of the four patients who developed RAS there was evidence of diminished allograft function. Successful correction of the stenotic lesion in these two recipients resulted in a return of the blood pressure, PRA, and biochemical function of the allograft to normal. Unsuccessful attempts at surgical repair led to loss of the allograft in the other two patients with RAS. Intrarenal vascular and/or parenchymal lesions were evident in the other three recipients with hypertension. Although an explanation was not apparent, subclinical rejection was hypothesized. Treatment effected reduction of the hypertension in these three patients and no deterioration of allograft function was observed for periods of 5, 34, and 38 mo, respectively. Renal angiographic studies and determinations of PRA are recommended in any pediatric recipient of an allograft who develops hypertension after the first month following transplantation or has hypertension which persists for longer than 6 mo after transplantation.