Introduction: Endodontic retreatment cases are usually associated with postoperative pain (PP) and inflammation, due to the accumulation of bacteria inside root canals such as the E. faecalis bacteria. High-level diode laser intracanal irradiation was proposed as an effective method of root canal disinfection and decreasing PP following the primary endodontic procedures. However, there is no relevant evidence about its effect in the retreatment cases. Aim: To evaluate the effect of 980 nm diode laser intracanal irradiation on postoperative pain and root canal disinfection in endodontic retreatment cases with chronic periapical lesions.