Objective: This study aimed to compare the serum oxidative stress levels of patients with adenotonsillar hypertrophy (ATH) with those of controls and to investigate the effects of adenotonsillectomy on the oxidative stress levels.Material and Methods: Thirty healthy children (mean age, 6 years) and 30 patients with ATH (mean age, 7 years) aged 2-12 years were included in the study. Serum total oxidant status (TOS), total antioxidant status (TAS), oxidative stress index (OSI), and paraoxonase (PON) levels were compared between the patient and control groups. The preoperative and postoperative levels were also compared within the patient group.Results: The TOS and OSI levels were significantly higher in the patient group than in the control group (p=0.007 and p=0.027, respectively). There was no significant difference between the patient and control groups in terms of the TAS and PON levels (p=0.399 and p=0.237, respectively). The TOS and OSI levels in the patient group were significantly higher in the preoperative than in the postoperative period (p=0.005 and p=0.023, respectively), whereas there were no significant differences in the TAS and PON levels between the preoperative and postoperative period (p=0.192 and p=0.262, respectively).Conclusion: These findings demonstrate that patients with ATH are exposed to high levels of oxidative stress and that adenotonsillectomy normalizes the oxidative stress.