The mediastinal lines visible at conventional radiography represent the interfaces between the mediastinum and adjacent lung parenchyma. Preservation, obliteration, thickening and distortion of these lines represent the key to detecting and localising mediastinal abnormalities on chest radiographs. The learning objectives of this review are to: illustrate radiographic anatomy of the mediastinum with particular attention to mediastinal lines; describe radiographic signs that allow identification of mediastinal abnormalities that are difficult to detect on conventional chest radiographs; describe findings that help localise abnormalities in the anterior, middle or posterior mediastinum. The anterior junction line obliteration, the hilum overlay sign, the preservation of the posterior mediastinal lines and the silhouette sign with the right cardiac border are radiographic signs that allow identification and localisation of anterior mediastinal lesions. Widening of the right paratracheal stripe, distortion of the azygo-oesophageal recess and the convex border of the aortopulmonary window indicate the presence of a middle mediastinal abnormality. Thickening, distortion or disruption of paraortic and paraspinal lines and posterior junction line obliteration are caused by posterior mediastinal lesions. Knowledge of normal radiographic mediastinal anatomy and mediastinal lines is crucial to identifying subtle mediastinal abnormalities that can be easily missed on conventional radiography. Moreover, this approach allows identification of the involved mediastinal compartment on chest radiographs, thereby directing the most appropriate further diagnostic workup.