Introduction:Usual treatment for patients with aldosteroneproducing adrenal adenoma is adrenalectomy, whereas adrenal hyperplasia is generally treated medically. Selective adrenal venous sampling (AVS) has been adopted to differentiate between adenoma and hyperplasia. A previous ratio used in our institution for the diagnosis of adenoma proved to be too low. As a result, a disproportionate number of patients with a preoperative diagnosis of adenoma were operated and subsequently found to have hyperplasia.