We present an unusual case of primary aldosteronism in childhood.A 9-year-old boy had hypertension, hypokalemia, hyporeninemia and hyperaldosteronism.Dexamethasone administration decreased plasma aldosterone transiently but failed to correct the hyperaldosteronism, excluding dexamethasone-suppressible hyperaldosteronism. Plasma aldosterone decreased with upright posture and showed a circadian rhythm. Spironolactone treatment normalized blood pressure and serum potassium and lowered aldosterone secretion.During the studies, plasma aldosterone correlated with serum cortisol but not with plasma renin. Preoperative results indicated that this patient presented the functional features of aldosteronoma.Adrenal computed tomography, scintigraphy and left venography were not diagnostic of adrenal lesions. The left adrenal venous sampling showed hypersecretion of aldosterone from the left adrenal gland. The left adrenalectomy revealed micronodular hyperplasia but resulted in a prompt and sustained reversal of hypertension and hyperaldosteronism. These findings suggest that primary aldosteronism in this patient resulted from primary adrenal hyperplasia.Thus, adrenal hyperplasia is a heterogenous group of disorders and carefully selected studies allow prospective selection of appropriate treatment. primary aldosteronism ; childhood ; primary adrenal hyperplasia Primary aldosteronism characterized by hypertension, hypokalemia and hyporeninemia is very rare in childhood (Grim et al. 1967 ;Ganguly et al. 1980b ;New and Levine 1980;Bryer-Ash et al. 1984;Oberfield et al. 1984). Typically, three forms of primary aldosteronism are identified : Aldosterone-producing adenoma (APA), idiopathic hyperaldosteronism (IHA) and dexamethasone-