A 22-year-old man with movement-dependent knee-joint pain was operated on for patellar chondroplasia and meniscal dysplasia after two previous arthroscopic removal of free joint bodies had failed to bring relief. A few months after the operation the same leg had become swollen with signs of venous congestion, long saphenous vein varicosity and traumatic pretibial crural ulcer. The long saphenous vein was partially excised. 18 months after the arthrotomy there was clinical and colour-Doppler evidence of an arteriovenous fistula with false aneurysm in the region of the popliteal artery as cause of the venous congestion. The ulcer healed completely after ligation of the fistula and excision of the false aneurysm. --Arterio-venous fistula should be included in the differential diagnosis as a possible cause of postoperative swelling of a limb.