Modern methods of root canal cleaning and filing are causing formation of the smear layer on treated surfaces. The aim of this paper was to review clinical aspect of smear layer in endodontics. Smear layer is the consequence of instrumentation of root canal walls and is consisted of organic and inorganic particles of cut dentine, necrotic and/or vital pulp fragments, microorganisms and their products. Existence of smear layer is affecting permeability of the radicular dentine, thus decreasing effects of canal medicaments and impairing adhesion of obturation materials in root canal. Removal of the smear layer from canal walls is possible with use of various chemical agents, ultrasonic or laser techniques. Regardless to contradictory attitudes and opinions, removing the smear layer is required for possible bacterial contamination, compromised effects of root canal medication and in order to obtain better obturation of canals 'system. .