Postoperative atelectasis is a common problem following any surgery. Limited atelectasis is usually well-tolerated and easily reversible. However, complete atelectasis of the remaining lung following partial lung resection may be poorly tolerated. Thoracic surgical procedures increase the risk because pain, thoracic muscle injury, chest wall instability, and diaphragmatic dysfunction impair clearance of secretions by cough. In addition, patients with lung diseases are prone to increased bronchial secretions. Prophylaxis includes preoperative and postoperative physiotherapy and medications, which should be graded in accordance to the individual patient's risk factors. Large atelectasis requires bronchoscopy to remove mucous plugs. Tracheostomy should be considered in patients with relapsing atelectasis or swallow disorders.