Background and Rationale: The proportion of hypertensive patients meeting the definition of resistant hypertension is growing rapidly as doctors use more combination antihypertensive treatments in order to reach lower target blood pressures. Spironolactone is often used in specialist clinics for patients with resistant hypertension although it is currently only licensed in the UK for use in hypertension complicated by primary hyperaldosteronism. Uncontrolled studies suggest that spironolactone is a very effective antihypertensive in the modern management of resistant hypertension but we could find no randomised trials in this setting. In the Sheffield Hypertension Clinic spironolactone is currently used as one of the drugs of choice in patients with resistant hypertension, particularly in women and is anecdotally often very effective.