Abstract Of the methods of detecting incompetent perforators in current use, only two, clinical and ultrasouna, are easily performed and lend themselves to routine use in the ward or outpatients' department. The ultrasound method has a higher degree of accuracy than the clinical method, requires little in the way of additinal equipment or training and provides a very useful method of pre- and postoperative assessment of the varicose leg as well as a method for the study of the natural history of the disease. In a pilot study of 100 limbs 28 incompetcnt perforators were discovered in 36 ‘normal’ limbs. A detection rate of 82 per cent in 165 marked sites was noted in limbs with varicose veins. Greater numbers of perforators were found in association with skin changes and previous operation than in uncomplicated varices. In 15 of 64 limbs with varicose veins no incompetent leg perforators were detected.