Usually, first mandibular molars have one mesial and distal root but in some cases there are anatomical variations. Presence of an additional lingual root distally in mandibular molars is called radix entomolaris (RE). If present, an awareness and understanding of this unusual root and its root canal morphology can contribute to the successful outcome of root canal treatment. The article describes the endodontic management of mandibular molar with RE.