Background: Primary aldosteronism is one of the most common forms of secondary arterial hypertension. Adrenalectomy is effective in patients with proven unilateral hypersecretion of aldosterone whereas pharmacotherapy is indicated in bilateral forms of the disease. We can meet the opinion that in patients with confirmed primary aldosteronism and finding ofsuprarenal adenoma > or = 1 cm on computed tomography (CT) scanning, adrenalectomy can be recommended without further investigation. On the other hand we can perform adrenal venous sampling (AVS) to prove unilateral overproduction of aldosterone., Objectives: To evaluate whether AVS is necessary in all patients with unilateral adenoma > or = 1 cm., Methods: We analyzed data from patients with proven primary aldosteronism, CT finding of adenoma > or = 1 cm along with normal morphology of contralateral adrenal gland, and successfully performed AVS., Results: Out of 107 patients with proven primary aldosteronism, indicated for AVS, we included 30 patients with CT finding of suprarenal adenoma > or = 1 cm along with normal morphology of contralateral adrenal gland and successful AVS. Unilateral overproduction of aldosterone was found only in 17 cases (56.7%), the results in remaining 13 patients (43.3%) did not confirm activity of adenoma., Conclusion: Our results support necessity of performing AVS in all patients with primary aldosteronism in whom surgical treatment is considered, CT confirmation ofan adenoma is insufficient in this indication.