
A comprehensive knowledge of the root canal anatomy is essential for successful endodontic treatment. However, presence of anatomic malformation in the tooth can be diagnostically and technically challenging and hence may pose difficulties during endodontic therapy. One such anatomical variation is the presence of extra root distolingually in permanent mandibular first molars. This additional root is called Radix entomolaris. Awareness and understanding of this unusual root and its canal morphology are factors that can affect the outcome of root canal treatment. This article presents a case of Radix entomolaris in a mandibular left first molar and knowledge about its prevalence, possible aetiology, external and internal morphology, radiographic and clinical approach to diagnosis, endodontic management and common iatrogenic errors which may occur during the treatment.