© 2020 Japan Pediatric SocietyBackground: Oxidative stress plays a role in the pathogenesis of many chronic diseases. Upper airway obstruction has been identified as a risk factor for increased oxidative stress-related disorders such as obstructive sleep apnea. The effect of adenotonsillar hypertrophy, which may result in a narrowing of the upper airways, on oxidative stress can be a valuable subject of research. This study aimed to investigate the efficacy of adenotonsillectomy on oxidative stress evaluated using the thiol / disulfide balance. Methods: Thirty children who underwent adenotonsillectomy and 30 healthy controls, all aged from 3 to 18 years, were included in the study. Blood samples were taken preoperatively and 3 months postoperatively in the study group; in the control group, baseline blood samples were taken and samples were again taken 3 months later. Thiol / disulfide homeostasis items were analyzed. Antioxidant markers were native thiol, total thiol, and native / total thiol. Oxidative stress markers were disulfide, disulfide / native thiol, and disulfide / total thiol. Results: At the preoperative period, oxidative stress parameters of thiol / disulfide homeostasis were higher in the study group than in the control group (P < 0.05) and antioxidant activity parameters were lower than in the control group (P < 0.05). Three months postoperatively, oxidative stress parameters were lower than in the control group (P < 0.05), and antioxidant parameters were no different from those in the control group (P > 0.05). In the adenotonsillectomy group considered separately, oxidative stress markers of disulfide and disulfide / native thiol decreased (P < 0.05) and antioxidant markers of native thiol and total thiol increased in the postoperative measurements (P < 0.05). Conclusions: Oxidative stress related to adenotonsillar hypertrophy decreased after adenotonsillectomy. The antioxidant parameters of the thiol homeostasis increased after adenotonsillectomy. We concluded that adenotonsillectomy operations should be planned and applied timeously to prevent the adverse effects of adenotonsillar hypertrophies on thiol homeostasis.