Mandibular molars display considerable variations with regard to the number of roots and root canals. One such anatomical variation is the presence of an additional root located distolingually, which is called radix entomolaris. An awareness and understanding of this unusual root and its canal morphology is important as it will contribute to the successful outcome of root canal therapy. This case report provides insight into the endodontic management of a mandibular molar with radix entomolaris, with the aid of spiral computer tomography. Schlagwörter: distolingual root, mandibular molar, radix entomolaris, spiral CT