An awareness and thorough knowledge of internal and external root canal morphology contribute to the successful root canal treatment. Mandibular first molars show most of the anatomical variations not only in the number of canals but also in the presence of number of roots and their morphology. The presence of additional root either lingually or buccally in addition to two roots is one of the complex morphological variations. Diagnosis, identification, and treatment of these variations need adequate knowledge of root and root canal anatomy and configurations which can contribute to the better outcome. This case report discusses the endodontic treatment of two mandibular first molars with a radix entomolaris (RE), with 3 roots and 4 root canals, which are rare macrostructures

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