Acute mediastinitis is a fatal infection which occurs related to connective tissue of mediastium, in the thoratic organs. Occurrence of mediastinitis due to craniocervical infection is very rare, and is defined as descending necrotizing mediastinitis. November 8th, 2008, man in his early fifties visited ER due to severe swelling on left neck area and dyspnea. Antibiotic were administered immediately, and vast amount of abscess formation on pneumomediastinum and adjacent tissues were observed via chest computed tomography. With cooperation of thoracic and cardiovascular surgery department, emergency incision and drainage with drain insertion was done to remove abscess, and control the infection. After surgery, everyday saline irrigation through drain was done during hospitalization, with continues antibiotic therapy. Descending necrotising mediastinitis is a most rare and dangerous infection which occurs on oropharyngeal area. In case of descending necrotising mediastinitis, accurate diagnosis, airway maintenance, remove of abscess by incision and drainage, aggressive antibiotic therapy and continuous saline irrigation is necessary to increase patient survivability. Also, computed tomography with contrast media is essential to figure out the size and location of the infection and abscess formation.