OBJECTIVE: Primary aldosteronism, an important form of secondary hypertension, is associated with significant increase of cardiovascular risk (ischaemic heart, cerebrovascular events, arrhythmias) (relative risk 4.6). The specific treatment of primary aldosteronism significantly reduces cardiovascular risk. In addition to high blood pressure values and direct action of aldosterone, new mechanisms such as increased oxidative stress are involved in the development of organ damage, metabolic, endothelial and coagulation complications. METHODS: The aim of the study was to evaluate parameters of oxidative stress in 38 patients (21 men, 17 women, mean age 53.3 ± 4.7 years) with primary aldosteronism [11 aldosterone-producing adenoma (APA) (4 men, 7 women, mean age 50.2 ± 4.5 years) and 27 idiopathic adrenal hyperplasia (IHA) (17 men, 10 women, mean age 54.5 ± 5.3 years)] at diagnosis and after specific treatment (surgical or pharmacological), with respect to 50 patients with essential hypertension (26 men, 24 women, mean age 49 ± 7.4 years) and 50 healthy individuals (28 men, 22 women, mean age 48.7 ± 4.4 years). RESULTS: Patients with primary aldosteronism showed significant increase of NADPH oxidase (Nox2-dp) plasma levels and urinary isoprostanes (34.9 ± 4.3 μg/dl and 216.3 ± 15.7 ng/mg, respectively; P