Mandibular first molars can show anatomical variations in the form of an additional lingual (radix entomolaris) or buccal root (radix paramolaris). The presence of an additional root can lead to difficulties during endodontic treatment. This case report describes the treatment of a first mandibular right molar with a small radix entomolaris. Keywords: anatomical variations, radix entomolaris, radix paramolaris, three-rooted mandibular molar