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Plasma aldosterone concentration/plasma renin activity ratio is widely used as a screening tool of primary aldosteronism (PA). We evaluated that plasma aldosterone concentration (pg/ml)/plasma active renin concentration (pg/ml) ratio >40 is useful for screening of PA among hypertensive patients. Subsequently, oral sodium loading test (10-12g NaCl for 3 days) is performed to the suspected PA patients and definite diagnosis of PA is made if 24-hr urinary aldosterone is more than 13-15 μg/day on the third day. In addition, furosemide loading test is also shown to be useful to make definite diagnosis of PA if plasma active renin concentration is still suppressed after 2 hr of furosemide administration. Subsequently, differential diagnosis whether unilateral or bilateral lesions should be determined in definite PA patients. If unilateral lesion is suspected by adrenal CT scan, ^I-adosterol adrenal scintigraphy should be performed. If adosterol is accumulated in the adrenal tumor detected by CT scan, laparoscopic unilateral adrenalectomy should be indicated without performing adrenal venous sampling (AVS). However, if adosterol scintigraphy shows other findings, such as bilateral or contralateral accumulation, ACTH-loading AVS should be performed to determine laterality of aldosterone production. Besides, when 24-hr urinary 18-hydroxycortisol (18-OH-F) is more than 0.2 mg/gCr, diagnosis of aldosterone-producing adenoma is indicated. When AVS is performed, hormonal laterality should be determined by aldosterone/cortisol (A/C) ratio in the adrenal veins and inferior vena cava. Lateralized ratio is calculated by A/C ratio of the tumor side-adrenal vein/A/C ratio of the nontumor side-adrenal vein. Contralateral ratio is calculated by A/C ratio of nontumor side-adrenal vein/A/C ratio of the inferior vena cava. Unilateral legion is indicated upon lateralized ratio >4 and/or contralateral ratio