Aim. This study was designed with the purpose to determine the relation between the great saphenous vein diameter and the success of sclerotherapy. Methods. A total of 136 legs were treated by foam sclerotherapy. The saphenus vein was cannulated ultrasound-guided 10 cm above the knee. Results. Complete closure of great saphenous veins was achieved with a single injection at 6 month follow up in 109 legs. Twenty seven legs got an incomplete closure. In those cases, the distance from closure to SFJ was from 15 to 20 mm, and the medium distance was 18.2 mm. Conclusion. Foam sclerotherapy is an effective, less expensive day care procedure with minimal complication rates. Patients treated by sclerotherapy with a GSV' diameter greater than 12 mm. and have more possibilities of no getting a total occlusion of GSV. Dis-apperance symptoms after sclerotherapy is not related with GSV' diameter.