Primary aldosteronism (PA) is the most frequent endocrine form of secondary hypertension. The recognition of this disease has dramatically increased with the widespread use of a screening test in most hypertensive patients, including those who are normokalemic. Interest in PA has grown since the demonstration that aldosterone has deleterious effects that are, at least in part, independent from its effects on blood pressure. The identification of the subtype of PA is fundamental to distinguish between subtypes that benefit from surgery and subtypes that should be treated pharmacologically with mineralocorticoid receptor antagonists. This article reviews the strategies to correctly identify PA subtypes, underlining the central role of adrenal vein sampling.