Improvement of failed root canal treatment is defined as retreatment, in endodontics. Retreatment is applied to teeth with chronic pain and symptoms after root canal treatment, or when root canal filling is technically insufficient, and when there is non-healing periapical radiolucency. If diagnosis is right and all the techniques are used carefully, conservative retreatment will be successful. There are lots of Ni-Ti rotary systems developed for retreatment. This study presents the three years follow-up of the retreatment cases with ProTaper Universal Retreatment system conducted on two patients who applied to the Erciyes University, Faculty of Dentistry; and obtained successful results.