Backgrounds: Altered sensation due to a nerve injury is an infrequent and severe complication of endodontic treatments. Altered sensation following endodontic treatment may result in liability claims. Hence; the present study was undertaken for assessing the incidence of altered sensation after mandibular premolar and molar peri-apical surgery. Materials & methods: A total 50 patients were enrolled in the present study that was scheduled to undergo peri-apical surgeries involving mandibular premolar or molar. All the surgeries were performed under the hands of skilled and experienced Endodontists. Patients were given a postoperative instruction sheet. Patients were informed of the possibility of altered sensation and advised to contact the clinic in case of untoward event. Incidence of altered sensation was recorded and analysed. Results: The overall incidence of altered sensation was found to be 22 percent (11 patients). Out of 26 cases of mandibular premolar involvement, altered sensation occurred in 34.62 percent of the cases. Out of 24 cases of mandibular molar involvement, altered sensation occurred in 8.33 percent of the cases. Incidence of altered sensation was significantly higher among patients undergoing peri-apical surgery involving mandibular premolar in comparison to mandibular molar. Conclusion: Peri-apical surgeries in the mandibular arch are significantly associated with altered sensation, particularly in mandibular premolars in comparison to mandibular molars. Key words: Altered sensation, Mandibular, Peri-apical surgery