The accuracy of Duplex ultrasound scanning in locating the sepheno-popliteal junction (SPJ) was assessed by comparison with clinical examination and short saphenous venography. Twenty-three legs with varicosities of the short saphenous system had their SPJ located by Duplex scanning and marked pre-operatively. Varicography was performed on all patients. Clinical examination localised the junction to within 2 cm in 8/23 (37%) compared to 16/23 (74%) for Duplex ultrasonography and 21/23 (93%) venography. Ihis study shows that Duplex ultrasonography while more accurate than clinical evaluation, should not replace venography in the pre-operative localisation of the SPJ.