Right middle lobe syndrome (RMLS) is a rare condition characterised by atelectasis of the right middle lobe of the lung, best seen on lateral chest radiograph as a wedge-shaped density that extends from the hilum anteriorly and downward. It is caused by a variety of etiologies including bronchiectasis, chronic obstructive lung disease and infection.

In adult patients, a history of recurrent attacks of cough, haemoptysis, dyspnoea and chest pain should be investigated. Symptomatic patients should be evaluated by a complete chest radiograph and computed tomography. A flexible bronchoscopy may be helpful in determining the patency of the middle lobe bronchus and identifying tumors or intrabronchial foreign bodies that can predispose to recurrent pneumonia.