OBJECTIVE To assess the technique of subfascial endoscopic ligation of incompetent perforatory veins by use of a mediastinoscope. METHODS Prospective open clinic study. METHODS Two Departments of Surgery. METHODS Thirty-eight consecutive patients (40 legs) with recurrent or protracted venous ulceration of the lower leg were treated. Through a short, transverse incision of the skin and fascia in the proximal 1/3 of the lower leg a mediastinoscope (length 18 cm, diameter 12 mm) is inserted after which the perforating veins are ligated by haemoclips under direct vision. RESULTS All legs showed signs of incompetent perforating veins by clinical examination, confirmed with continuous wave ultrasonography and in 31 legs there was associated deep vein incompetence. Sixteen patients had active ulceration at the moment of operation and 22 had a history of recent or recurrent ulceration. One patient developed an inflammatory reaction at the wound and in two legs a subfascial infection occurred, necessitating surgical drainage. No postoperative mortality was seen. All 16 ulcers healed within 2 months (mean: 34 days; range: 21-55 days). During a mean follow-up of 3.9 (range: 2-5) years only one out of 38 patients (2.5%) developed a recurrent ulcer. CONCLUSIONS Subfascial endoscopic ligation of incompetent perforating veins by use of a mediastinoscope is a relatively simple technique with a low postoperative complication rate and a low recurrent ulcer rate which makes it a valuable method for treating incompetent perforating veins.