Valvular lesions of the main venous stems are regarded as the predominant cause of the formation of primary varicose veins. Peripheral arteriovenous shunts are regarded as sequelae of varicose veins rather than their cause. The perforating and communicating veins are not involved in the pathogenesis of varicose veins. This opinion is supported by the demonstration of insufficiency of the main superficial venous stems in a series of 200 consecutive cases of primary varicosis, even if only the more peripheral veins were dilated. In addition, histological examination of the uppermost valves in the saphenous veins of patients and experimental studies on post-thrombotic vein valves corroborated these views. The therapeutic importance of high ligature of the saphenous veins is stressed. Removal of the dilated veins by stripping is best, but unnecessarily radical procedures should be avoided. A combination of stripping with sclerotherapy is recommended. The dangers of both forms of treatment are outlined.