Introduction: The objective of this study was to evaluate the effect of fixed appliances on oral malodor. Methods: Forty-one patients participated in this study. They were randomized into 2 groups: treated with fixed orthodontic appliances and untreated controls. Oral malodor measurements and the gingival and plaque indexes were recorded in each group by same periodontist. Measurements were taken from the study group before bonding, 1 week after bonding, and 4 weeks after bonding. The control group's measurements were made at the same time. Results: Oral malodor and the gingival and plaque indexes were significantly increased 1 week after bonding (P <0.05). Oral malodor was increased at 4 weeks after bonding (P >0.05). The comparison of the groups showed differences 1 week and 4 weeks after bonding. Conclusions: The oral malodor reached the critical level during fixed orthodontic treatment. Oral malodor could indicate a need to evaluate oral health and remind patients of the importance of maintaining ideal oral hygiene. Copyright © 2011 by the American Association of Orthodontists.