We report on the application possibilities of sonography in phlebology. Sonographic examination of 131 lower legs showing various clinical forms of chronic venous insufficiency is discussed. Ultrasound offers a timesaving, non-invasive, and reproducible technique to detect insufficiencies concerning orifice or trunk of the great and lower saphenous veins as well as the perforating veins. The method allows varying diagnostic sensitivities. Thrombotic changes in the deep veins may be demonstrated with relative accurateness. As to insufficiencies concerning the epifascial and perforating venous system (in epifascial chronic venous insufficiency, stage I to IV), the question of surgical or sclerotherapeutic treatment can be settled in most cases according to the sonographical findings alone. Subfascial forms of chronic venous insufficiency require additional invasive diagnostic techniques, such as plethysmography, phlebography, and venous pressure measurements. In consideration of the high diagnostic importance of ultrasound, sonographic devices should be available and applied in a large number of phlebologic practices.