Descending necrotising mediastinitis (DNM) is a type of mediastinitis caused by head and neck infections, which spreads to the mediastinum via the cervical fascial planes. This infection is a rarely reported but highly lethal infection. Computed tomography was used to diagnosis the disease and assess the efficacy of treatment. Delay in diagnosis and insufficient drainage of the mediastinum and deep neck infection are the main causes of mortality in DNM. We report on a case that was treated successfully, even if with a long, protracted course.