Sclerotherapy consists of injecting a sclerosing product (in liquid or foam form) into the varicose vein which causes its permanent closure, or its sclerosis. As it is simple and safe, this treatment is by far the most frequently prescribed. It is ideal for treating small to medium sized varicose veins. However, the larger the varicose veins, the more its effectiveness decreases. This is especially true when the diameter of the varicose veins exceeds 5 to 6 mm. In such cases, the sclerosis may only be partial, and may give rise to complete relapses. Thanks to venous ultrasound, it is now possible to measure the diameter of the veins before prescribing the most appropriate treatment to be adopted.