Relevance. Dental, periodontal and tonsillar infections remain a serious clinical problem, sometimes causing complications and requiring hospitalization. They cause purulent fusion of the face, neck tissue and distant spaces, including mediastinum.Aim. To present a clinical case showing the successful treatment of odontogenic descending necrotizing mediastinitis.Materials and methods. Patient medical history. The present disease history. Direct clinical evaluation. Clinical laboratory and X-ray data (SCT – spiral computed tomography). The case was diagnosed with chronic periodontitis (stage IV, grade C) and periodontal abscess of tooth 37. Floor-of-the-mouth phlegmon left parapharyngeal space phlegmon. Phlegmon within cervical space. Mediastinitis. Surgery. General anaesthesia. Extraction of tooth 37. Drainage of subgingival and parapharyngeal abscesses and drainage of phlegmons within the submandibular and the right-side cervical space. Mediastinum drainage.Conclusion. The proposed patient evaluation technique established diagnosis and adequate surgical treatment allowed the achievement of successful treatment outcomes, confirmed by clinical and X-ray data and patient self-evaluation of the disease's internal picture (PSAF-auto-maladaptation).