Primary aldosteronism (PA) is one of the potentially curable forms of hypertension. The hypertension is secondary to aldosterone action in the kidney, reabsorbing sodium and water that increases the intravascular volume and blood pressure. PA was previously believed to account for less than 1% of hypertensive patients when hypokalemia is used as screening method. However, recent studies using the plasma aldosterone to renin activity ratio (ARR) as screening test have demonstrated a high prevalence of PA in hypertensive populations. This prevalence vary depending on the severity of hypertensive disease being higher in stages 2 (8.55%) and 3 (13.5%) of the disease. Only a small proportion of PA patients (between 9 and 37%) are hypokalemic. The diagnosis of PA is advocated to confirm the autonomy of aldosterone secretion from the renin-angiotensin system and to differentiate the clinical subtypes of the disease. The most common subtypes of PA are idiopathic aldosteronism and aldosterone-producing adenoma. Other causes are glucocorticoid-remediable aldosteronism, unilateral or primary adrenal hyperplasia and adrenal carcinoma. This article reviews the new data about prevalence, diagnosis criteria and describes the clinical, biochemical and genetic characteristics of the different subtypes of the disease.