Rationale: Primary hyperaldosteronism (PA) is the most frequent form of secondary hypertension. In PA autonomous hypersecretion of aldosterone by one or both adrenal glands causes hypertension that is often refractory to treatment. PA is usually caused by either a unilateral aldosterone-producing (micro)adenoma (APA) or by bilateral adrenal hyperplasia (BAH). Distinction between APA and BAH is critical since the former is treated with the aim of cure by adrenalectomy, and the latter by mineralocorticoid receptor antagonists. This distinction can be made by adrenal vein sampling (AVS), as recommended by The Endocrine Society 2008 guideline or by CT-scanning, as is common practice in the Netherlands. AVS is invasive, demands great skill, and is expensive, while CT-scanning is non-invasive, easy and cheap, but might be less accurate. However, the advantage of AVS has never been demonstrated in prospective randomized studies. Here we propose to perform a prospective, randomized, multicenter study that compares effectiveness of AVS with effectiveness of CT-scanning for the diagnosis of PA subtype.