Elevated blood pressure (160/120 mm Hg) was found in an 8 1/2-year old body and remained unchanged during the following 3 years. The only abnormal findings were undetectable plasma renin activity (PRA less 0.16 ng/ml-3 h) even after sodium restriction and upright posture and a slight tendency for hypokalemia (3.7 mEq/1, lowest value 3.3 mEq/1). Plasma aldosterone (PA) and plasma cortisol (PC) were normal. Administration of dexamethasone and spironolactone resulted in only a minimal decrease of blood pressure whereas hydrochlorothiazide was slightly more effective. The circadian rhythm of PRA, PA and PC was studied by otaining frequent blood specimens during one night. The diurnal variation of PA and PC was normal despite undetectable PRA (less than 0.16 ng/ml-3 h). Primary aldosteronism and other conditions associated with mineralocorticoid excess were excluded. The patient seems to represent an example of low renin essential hypertension. This is the second recorded case of this syndrome in childhood.