Patients with primary aldosteronism do not have distinctive clinical features. However, the associated hypertension is invariably high and often resistant to drug therapy. The recommended initial test in suspected primary aldosteronism is the determination of aldosterone excretion rate after salt loading. Patients in whom aldosterone excretion rates exceed 14.0 micrograms per 24 hours when the urinary sodium is at least 250 mEq per 24 hours are prime candidates for additional studies. The presence of hypokalemia and/or suppressed plasma renin activity provides corroborative evidence of primary aldosteronism, but the absence of either or both does not preclude the diagnosis. Spontaneous, moderately severe hypokalemia (less than 3.0 mEq per L), an anomalous postural decrease in plasma aldosterone concentration, and increased plasma 18-hydroxycorticosterone values (greater than 100 ng per dl) indicate the presence of an adenoma. For localization of an adenoma, an adrenal CT scan should be obtained first and is considered diagnostic if an adrenal mass is clearly identified. When the CT scan is inconclusive, adrenal venous sampling can be done for more definitive localization. In the presence of an adenoma, surgical excision is the recommended approach but only after pharmacologic normalization of arterial pressure and correction of metabolic abnormalities. Sustained salt and water depletion is the most important therapeutic goal for these patients, and cure can be achieved despite prolonged and severe hypertension.