Objective: To determine the possible role of oxidants and antioxidants in the pathogenesis of chronic tonsillitis (CT) and adenoid hypertrophy (AH) in children. Methods: Randomized, prospective, controlled. The study group was made up of children with chronic tonsillitis and adenoid hypertrophy who are to undergo tonsillectomy and adenoidectomy. The control group was constructed with otherwise healthy children with normal ENT examination. The blood levels of antioxidants (retinot, beta-carotene, alpha-tocopherol, laycopene, ascorbic acid, superoxide dismutase, glutathione peroxidase, GSH) and peroxidation products (malondialdehyde) were determined before and 1 month after the operation in the study group and once only in the control group. These antioxidants and peroxidation products were also measured in the tonsil and adenoid tissue that were obtained during operation. Results: In the study group, the blood levels of antioxidants and oxidant before and after the operation were significantly different when compared to the control group (P < 0.05). In the study group, the blood antioxidant levels increased and oxidant level decreased significantly after the operation (P < 0.05). These levels after the operation never reached those of the control group. Conclusions: Oxidants and antioxidants played a significant role in the pathogenesis of chronic tonsillitis and adenoid hypertrophy in children. These children are under significant oxidative stress. Tonsillectomy and adenoidectomy significantly decreased the oxidative stress in these patients, but could not normalize it completely. Further studies are necessary to evaluate their possible therapeutic role in preventing recurrent tonsillitis and treating postoperative patients to help normalize their blood levels of antioxidants. (C) 2004 Elsevier Ireland Ltd. All rights reserved.