Purpose: To evaluate the changes of Oral Health Related Quality of Life (OHRQoL) in patients after the placement of a fixed orthodontic appliance. Materials and Methods: This prospective study consisted of 148 adolescents (97 girls and 51 boys) between the ages of 14 and 17 who were patients of an orthodontic clinic. OHRQoL was assessed by a modified questionnaire that evaluated four domains: oral symptoms, functional limitations as well as emotional and social well-being in three time frames: before bonding and banding (T0), two months after initiating orthodontic treatment (T1) and six months after initiating orthodontic treatment (T2). The repeated measures test was used to compare the relative changes of OHRQoL among the different time frames. Results: There were no significant differences between the levels of OHRQoL and its domains for boys or girls at any time point. The overall level of OHRQoL decreased significantly at T1 relative to T0; however, the emotional well-being domain improved at T1 in comparison to T0. At T2, the OHRQoL level increased significantly relative to T0 in all domains. Conclusion: The patients' quality-of-life level decreased by initiating orthodontic treatment; however, during that period, emotional well-being increased. As orthodontic treatment progressed, the quality of life level increased. Keywords: oral-health related quality of life, orthodontic treatment, patient assessment