Purpose of this study was the assessment of the anatomo-pathological modifications of the vein after EndoVenous Laser Treatment(EVTL) and, consequently, to understand if possible the mechanism of vein occlusion. After an unsuccessful EVLT we performed a standard great saphenous vein (GSV) stripping and examined microscopically the stripped GSV. A circumferencial vein wall damage was never observed; the damage was limited to a relatively small portion of the vein wall (about one third of it) and it did not interest all the wall layers. In conclusion, a widespread damage of the vein wall seems to be necessary to obtain vein occlusion. About the most likely mechanism of occlusion after EVLT, thrombosis of the vein lumen or edema of the vein wall, no definitive conclusion can be drawn.