Moderate or severe hypertension occurs in a small percentage of hypertensive children, but it is within this group that the surgically correctable causes of hypertension are found. Since cure rates up to 90% have been reported, it is important to diagnose a secondary cause of hypertension. Excretory urography is recommended to screen for renovascular hypertension and renal parenchymal disease. Renal scintigraphy can be substituted for the urogram, but the anatomical resolution is poorer. If renovascular hypertension is suggested by abnormal results of screening examination, arteriography should be part of the evaluation. Ultrasonography is reserved primarily for evaluating neonatal hypertension which most frequently is related to thrombosis. If this diagnosis is documented, renal function should be assessed with radionuclide techniques. If a hormonally active tumor is suspected, evaluation of the adrenals and retroperitoneum is accomplished best by CT.