Various factors may affect the outcome of root canal therapy. In this study 74 endodontocally treated pulpless teeth were evaluated: (43 with periapical radiolucency and 31 without periapical lesions). These 74 non surgical treatment were performed in 60 patients (26 men and 34 women) by undergraduated students. The overall success rate was 71.62%; the rate of success for cases with no periapical radiolucency exceeded 80% whereas only 62.8% of the cases with perapical radiolucency had undergone partial resolution or complete resolution. Only 17.1% of lesions demonstrated complete radiographic resolution 12 to 16 months after the endodontic treatment. Reasons that may explain the low success rate are lake of asepty, root canal preparation and root canal filling technique.