Statement of Problem: Flare up is an acute exacerbation of an asymptomatic pulpal and/or periapical pathosis after commencement or termination of root canal therapy. Its incidence may be different in patients treated by different practitioners regarding their graduation status.Purpose: The aim of this study was to compare flare up incidence in patients treated by dental students of Shiraz Dental School and those whom were treated by endodontists.Materials and Method: Patients' information including age, gender, and previous history of pain and pulp vitality were taken before treatment of 383patients. 230 of them were treated by senior dental students of Shiraz Dental School and 153of them were treated by endodontists. Students employed conventional step back technique whereas specialists had a chance to select variety of techniques. Data, regarding the quantity of pain experienced by patients were collected 48 hours after treatment. Case was considered a flare up if the patient had experienced severe pain which hadn’t been reduced either by analgesic medication or by consequent swelling. Chi- square statistic tests were used to analyze the receiving data.Results: 41 individuals (10.7%) out of 383 patients depicted flare up. 13.5% of these patients were treated by students and 6.5% were treated by endodontists. The difference was statistically significant.Conclusion: Different rate of flare up in two groups is probably due to the dissimilarity in skills, techniques and materials used by different operators.