Mediastinitis refers to inflammation of the tissues located in the middle chest cavity. It can be secondary to infectious or non-infectious causes and depending on the aetiology may be acute or chronic. The majority of cases of acute mediastinitis are secondary to oesophageal perforation and open chest surgery. Less common causes include tracheal, bronchial perforation or direct extension of infection from adjacent tissues. Chronic or slowly developing mediastinitis mostly arise from tuberculosis, histoplasmosis, other fungal infections, cancer, or sarcoidosis. In a minority of cases the aetiology is lymphatic obstruction or an autoimmune disease. Radiological imaging plays an essential role in the diagnosis and therapeutic approach to mediastinitis. Generally, the initial radiological work-up includes radiographic studies either with or without contrast material. However, conventional chest radiography may be misleading in the diagnosis of mediastinitis. Cross-sectional imaging techniques are generally required for diagnosis and evaluation of the site and extent of mediastinal involvement. Computed tomography and magnetic resonance imaging may also guide the choice of the optimal therapeutic approach. (C) 2004 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.