The aim of this study was to evaluate the accuracy and sensitivity of colour Doppler ultrasonography for the diagnosis of postoperative recurrent varicose veins in patients submitted to surgical ligation of the saphenofemoral junction with a view to classifying the recurrences according to the causes. We studied 401 lower limbs in the orthostatic position with colour Doppler ultrasonography in 318 patients (64 M and 254 F) presenting postoperative varicose vein recurrence during the follow-up (12-60 months). We evaluated the type of reflux at the inguinal level under the Valsalva manoeuvre and divided them into 5 types. We observed an incomplete crossectomy (type 1) in 23.2% of the cases; an incontinent saphenofemoral junction, intact and in an anatomical site in 12.5% (type 2); a major tributary (double saphena) originating from the common femoral vein near to the crossectomy site in 10.2% (type 3); neovascularization in 9.7% (type 4) and the presence of a number of major tributaries from the veins of the perineal and pudendal region or from the abdominal parietal veins in 44.4% (type 5). In all cases it was possible to note and classify the type of recurrence. Colour Doppler ultrasonography is an accurate, reliable tool for the diagnosis and classification of postoperative varicose vein recurrences in patients submitted to surgical obliteration of the saphenofemoral junction. It is decisive in the preoperative evaluation and follow-up of patients. In our experience, more than one half of the cases of recurrence were not due to an error of surgical technique.