Mandibular molars can have an additional root located lingually i.e. the radix entomolaris or buccally i.e. the radix paramolaris. Radix Entomolaris (RE) is a developmental variation occurring in mandibular molars associated with extra root and extra canal that is present lingually. An awareness and understanding of this variation and its root canal morphology is very important and play a very important role in having the treatment successful. Knowledge about its prevalence, diagnosis, morphology, canal configuration and clinical approach helps in achieving the endodontic success in clinical approach. This article presents a review of the clinical approach and a case series on the detection and endodontic management of radix entomolaris in mandibular first molars. Also added the modifications in the canal preparation, problems encountered during the treatment, common iatrogenic errors that occur during the treatment and factors which affect the prognosis. The prime failure to achieve success can be due to unusual tooth morphology.