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Background and purpose: Since there is a few studies about the reasons of endodontic treatment in Iran, it is necessary to evaluate factors and patients informational rate in all geographic regions for prevention and suitable treatment. So we decide to evaluate the reasons of endodontic treatment in patients who referred to endodontic group. Materials and methods: A descriptive cross-sectional study was carried out on 1,150 cases of Department of Endodontic in Babol dental school for each case, information was collected in a questionnaire including clinical and radiographic and systemic status of patients. Data were analyzed by statistical methods. Results: Out of 1150, 858 cases were perfect which were analyzed. Of the 858 treated teeth, 328 (36.8%) were males and 530 (59.6%) were females. The reasons for endodontic treatment were carries (82.2%), retreatment (7.2%), endo for prostheses (5.6%), restorative reasons (2.1%), trauma (2.8%) and periodontal disease (0.1%). Endodontic treatment was done in first and second and third molars in 42.9%, 16.2%, and 2%. There are in radiographic view 60.6% normal appearance, 18.4% periapical radiolucency, 15.4% widening of PDL and 0% root fracture. Systemic disease was 14.4% in patients with root canal therapy (RCT). Pain with cold, warm and endo for crown was 51.5%, 28.7%, and 1.4%, respectively. Conclusion: The most common reason for attending to dental school was pain. The most common and uncommon reasons for RCT were dental carries and periodontal disease. The most common and uncommon teeth were first and third molar. Pain with cold and endo for crown were the most common and uncommon findings.