Accurate knowledge of canal anatomy is one of the keys to success when performing root canal treatment. A succuessful outcome depends on three-dimensional debridement and obturation of the root canal system, maintained by a good coronal seal. Intimate knowledge of canal confluency is very important in order to shape the root canal system in the best possible way, and appreciation of uncommon anatomy allows the endodontist to conserve dental tissue. Moreover, using nickel-titanium (NiTi) rotary files, apical confluences and the acute angles of root curvatures often carries a high risk of instrument separation. The aim of this paper is to describe the root canal anatomy of mandibular molars. Keywords: endodontic anatomy, NiTi instrument failure, root canals