Despite numerous theories, the etiology and pathogenesis of primary varicose veins remain unclear. The etiology of chronic venous diseases (CVDs) known as chronic venous insufficiency (CVI) is related to leukocyte trapping. Leukocyte trapping involves trapping of white cells in vessel walls followed by their activation and translocation outside the vessel. Release of reactive oxygen species (ROS) from trapped white cells has been documented. Superoxide dismutase (SOD) directly inhibits the generation of free radicals and compounds that are produced during oxidation by ROS, such as malonyldialdehyde (MDA). The aim of this study was to determine the involvement of free radicals in the etiology of venous changes. The following material was used for the study: fragments of sufficient or insufficient venous system and varices from 31 patients diagnosed with chronic venous disease in the 2nd or 3rd degree, according to clinical state, etiology, anatomy and pathophysiology (CEAP), which were qualified for surgical procedure. The levels of oxidative stress markers strongly correlated with lesions observed by USG in insufficient and varicose veins. In both a higher concentration of MDA was observed, which is a sign of lipid peroxidation. Antioxidative mechanisms, SOD activity and total antioxidative power expressed as FRAP were inversely proportional to MDA concentration. In insufficient and varicose veins both FRAP and SOD activities were significantly lower than in normal veins. The severity of clinical changes was inversely dependent on the efficiency of scavenging of ROS, which additionally proves the participation of free radicals in pathogenesis of CVDs.