1. The clinical problem of varicose veins and so-called varicose ulcers is discussed. 2. The relationship of many of these ulcers to previous deep thrombosis is stressed and the evolution of the post-thrombotic leg from the acute stage to the chronic stage with central recanalised vein is illustrated. 3. The help given by the Valsalva technique in differentiating these cases with large, patent, valveless femoral veins, from those with normal valves is shown. This problem has been one of the main stumbling blocks in selecting patients for deep vein ligation. 4. The part played by the perforating veins in the lower third of the leg in the genesis of ulcers is mentioned. A venographic technique for showing these veins is given, and illustrative radiographs are shown.