This paper is the first of a series of articles on sclerotherapy. This method, also known as obliteration, is mainly used in the treatment of telangiectasias, venulectasias and reticular veins. It is based on blood flow depletion related to chemical processes. Osmotic agents, detergents and caustic agents are among those used for sclerotherapy. There are various contraindications for sclerotherapy and therefore it is very important to perform a precise qualification of patients. Moreover, the proper selection of agent concentrations, procedure technique and management after the sclerotherapy essentially influence the effectiveness of treatment.