Mediastinitis is a serious infection involving mediastinal spaces after cervical infections spread along the facial planes. A late diagnosis of mediastinitis may result in death. Here we present a diabetic patient suffered from mediastinit accompanied with hyperosmolar nonketotic coma. A 61 years old male patient with type 2 diabetes was admitted to our hospital, with complaint of generalized worsening and fever. A diagnosis of nonketotic hyperosmolar coma was done and proper treatment started immediately. Neck tomography revealed abscess formation in the upper mediastinum. The needle aspirat culture failed to show bacterial growth. After five days of antibiotic treatment the patient's symptoms resolved. The abscess formation and pleural effusion almost disappeared on control tomography. No similar case presentation was seen in the current literature. Apart from this case, mediastinit should be keep in mind when a patient suffered from dysphagia, fever and cervical swelling.