Purpose: To assess the effect of rapid maxillary expansion (RME) on the inflammatory and stress response of patients undergoing orthodontic treatment. Methods: Eighty salivary samples were collected from patients (n=16) during RME at five moments: before the expander placement (T1); 25 minutes after its first activa- tion (T2); seven days after placement, shortly after the patient arrived at the dental clinic (T3); 25 minutes after the appliance activation on day seven (T4) and one month after the last activation of the appliance (T5). Cortisol and nitric oxide levels were evaluated using an immunoassay kit and the Griess method, respectively. Friedman and Wilcoxon tests were used for statistical analysis (P <0.05). Results: Participants' mean age was 11.5 years. There was a significant change in cortisol levels over the study period in the total sample (P<0.01), for the Haas appliance (P=0.01), female sex (P=0.01), younger children (P=0.01), presence of large overbite (P=0.02), presence of posterior crossbite (P =0.006), Class I type occlusion (P=0.02) and mesofacial facial type (P =0.02). Regarding nitric oxide, there was a significant change over the study period in those who wore the Haas appliance (P =0.04). For nitric oxide levels, T1 was significantly higher than T3, T4 and T5 (P <0.05) for those who wore a Haas appliance. Conclusion: The period anticipating the consultation at the waiting reception area was more stressful than the dental procedure in patients undergoing RME. This procedure did not cause alterations in salivary biomarkers related to inflammation.