Descending necrotic mediastinitis is a serious illness which, among others, follows acute bacterial infections located in a cervical area. One of the most frequent causes of this illness, not connected with surgical interventions, is a peritonsillar and peridental abscess. The process originally placed in the peritonsillar area spreads along the cervical fascia engulfs mediastinum. Inflammatory process of the mediastinum considerably worsens the prognosis and obligates to decisive surgical (mediastinum drainage) and pharmacological (antibiotic therapy) treatments. The following works presents the course of the illness of a 55-year-old man who was diagnosed with severe sepsis in the course of the peritonsillar abscess. After surgical provision of the abscess (incision) the patient was qualified for the therapy with activated protein C (Xigris, Lilly). The patient condition initially improved, however, after 8 days a descending necrotic mediastinitis with ambilateral pleural abscess was diagnosed. The administration of the treatment within 48 days of hospitalization (antibiotic therapy, thoracotomy, flow drainage of the mediastinum, tracheotomy, respirotherapy) brought about the effect of complete recovery.