A 19-month-old boy presented with failure to thrive and polydipsia. Low-renin hypertension was diagnosed by the presence of hypertension, hypokalaemic alkalosis, suppressed plasma renin activity and low plasma aldosterone. Plasma levels and urinary excretion of other mineralocorticoids and glucocorticosteroids were low or normal. Urinary tetrahydrocortisol (THF) was increased relative to tetrahydrocortisone (THE) and also the plasma cortisol to cortisone ratio was elevated. These findings are suggestive of a decreased activity of cortisol-11β-hydroxysteroid dehydrogenase. Hypertension and hypokalaemia were not influenced by spironolactone and dexamethasone. Triamterene normalised serum potassium, but addition of furosemide was required for lowering blood pressure. With this treatment catch-up growth was observed.