Sclerotherapy is an important part of the treatment of varicose veins. It may also be performed in patients with contraindications for operative procedures. By adjusting the mode of application (liquid or foam) and the concentration it can be used for the treatment of all vein types. In comparison to other treatment options it is especially well suited for the treatment of spider veins and reticular veins, pudendal varicosity and so called "feeding" varicose veins in the proximity of venous leg ulcers. A current European guideline, which was approved by 23 European phlebologic societies, supports the good international standardization of this treatment technique.