Incompetent communicating or perforating veins are often responsible for recurrent varicose veins with skin changes at the lower leg, especially in the postthrombotic syndrome. Subcutaneous and subfascial surgical explorations carry a 35% complication rate. We used a new endoscopic technique to locate and ligate communicating veins with the objective to decrease this complication rate. Through a short skin incision on the anteromedial side of the proximal 1/3 of the lower leg the fascia is incised over 2 cm and the subfascial space opened by finger dissection. A mediastinoscope (length 18 cm; diameter 12 mm) is inserted and pushed down beneath the fascia to the level of the malleolus. Under direct vision the communicating veins crossing this space are located and ligated with haemoclips. In 48 patients, 15 male and 33 female, with a mean age of 53 (22-73) years, 54 legs were treated: 40 legs showed recurrent varicose veins, due to incompetent communicating veins with severe skin changes and ulcers, and 14 had primary varicosis. All patients complained of fatigue and pain. In 49 legs (44 patients) relief of preoperative complaints was obtained and in 5 (4 patients) there was no change. Two indurated wounds and 1 dehiscent wound were treated conservatively. One patient, operated on both legs, developed a severe subfascial infection on both sides necessitating a reintervention. The advantages of the subfascial endoscopic technique, a fast operative procedure, fewer postoperative wound infections (9.3%), a good cosmetic effect, and a low (2.5% after 3.8 years) recurrent ulcer rate make it a valuable new method for treating incompetent communicating veins.