Halitosis is a widely spread condition. There are numerous causes. The aim of this study was to investigate the influence of fixed orthodontic appliances on the occurrence of halitosis. 55 patients in an orthodontic practice were monitored at three points in time after application of orthodontic appliance (T1: immediately after application, T2: 4 weeks after application, T3: 3 months after application). Monitoring included patient self-evaluation, plaque index, tongue coating index and organoleptic measurement. The subjective parameters taste, dry mouth and breath odor did not show statistical differences. However, with the presence of fixed orthodontic appliances, confidence when performing dental hygiene decreased statistically significantly (p = 0.003). Additionally, the tongue coating index showed a statistically significant difference between T1 and T2 (p = 0.012) as well as T1 and T3 (p ⟩ 0.001). Analogous results were found for organoleptic measurement (T1 and T2 [p = 0.002]; T1 and T3 [p ⟨ 0.001]) and plaque index (T1 and T2/ T3 [p ⟨ 0.001]). Fixed orthodontic appliances lead to a statistically significant increase of the plaque and tongue coating indices. A statistically significant increase was also observed with organoleptic measurement scores. The suspected positive correlation between halitosis and fixed orthodontic appliances was confirmed. Halitosis can be an important indicator of oral health during orthodontic treatment and can serve as a motivating factor for adequate patient oral health care maintenance.