INTRODUCTION: Advantages of endodontic treatments over tooth extraction have increased the demands for these treatments. Success rate of these treatments is generally lower than the primary root canal therapies. Recently, single visit treatments have gained more popularity. But, the influence of completing retreatment in a single appointment on success of the treatment is still a controversy. The aim of this study was evaluating the most common causes of failures and determining the success rate of completing retreatments in single appointment. MATERIALS AND METHODS: Hundred and twenty four patients who had single appointment retreatment within past 4 years in postgraduate ward of Shaheed Beheshti Dental School were selected and clinical and radiographic examinations were carried out. The data were analyzed by SPSS using Chi-square and Exact Fisher tests. RESULTS: Success rate and uncertain cases were shown to be 50.7% and 34.2%, respectively and failure rate was 15.1%. Presence of periradicular lesion or history of swelling prior to retreatment had significant effect on the success of single visit retreatments (p<0.001). Another important finding of the study was that the success rate of retreatments was significantly higher in cases referred for restorative purposes compared with retreatments for nonrestorative purposes (p<0.001). CONCLUSION: The overall success rate of single appointment retreatments is up to 84.9% which is considerably higher in cases referred for restorative purposes. So based on the results of this study single appointment retreatment of symptom less teeth is recommended.