Recent clinical trials suggest that resistant hypertension is increasingly common. In the majority of patients, uncontrolled hypertension is due to persistent elevation of the systolic blood pressure. Older age and obesity are associated with poor blood pressure control. Other contributing factors include severity of the underlying hypertension and renal insufficiency. Poor patient adherence is thought be a common cause of medication resistance. Exogenous substances such as nonsteroidal anti-inflammatory drugs, oral contraceptives, and sympathomimetic agents can interfere with treatment. The prevalence of secondary causes of hypertension increases with age, especially atherosclerotic renal artery stenosis. Recent reports suggest that primary aldosteronism may be the most common secondary cause of hypertension. It should be considered in all patients with resistant hypertension. Effective treatment of resistant hypertension requires identification and reversal of contributing factors and/or secondary causes of hypertension. Pharmacologic therapy should utilize combination therapy, including a long-acting diuretic.