OBJECTIVE The aim of the study was to investigate a new possible background of increased risk of cardiovascular events in two forms of endocrine hypertension: in primary aldosteronism (PA) and pheochromocytoma/paraganglioma (PPGL) in comparison to essential hypertension (EHT). CONTEXT Prothrombotic properties of the fibrin clot structure, impaired fibrinolysis and enhanced thrombin generation have been reported to be associated with increased cardiovascular risk. DESIGN Patients with PA and PPGL were evaluated at baseline and re-evaluated 3 months after causative treatment. At baseline PA and PPGL patients were compared to matched EHT patients and to healthy controls. PATIENTS The study included 35 patients with PA, 16 patients with PPGL and two reference groups of patients with EHT (32 and 22 patients) and healthy controls (35 and 23 subjects). MEASUREMENTS All subjects underwent evaluation according to the study protocol that included plasma fibrin clot permeability (Ks), clot lysis time, endogenous thrombin potential. RESULTS There were no differences in clot structure and fibrinolytic activity in PA and PPGL patients as compared to matched patients with EHT, whereas all hypertensive groups were characterized by more compact fibrin clot structure, faster clot formation and enhanced thrombin generation in comparison to healthy controls. Both in PA and PPGL patients, fibrin clot properties and fibrinolytic parameters remained stable after the causative treatment. CONCLUSIONS Patients with PA and PPGL are at a prothrombic state comparable to patients with EHT. The results suggest the higher risk of cardiovascular events observed in hypertensive PA and PPGL as compared to EHT is not mediated through investigated prothrombic mechanisms.