Unilateral hyperlucent hemithorax is a frequent chest radiographic finding in the pediatric population. There is a wide spectrum of differential diagnoses, including congenital and acquired conditions involving the pulmonary parenchyma, airways, pulmonary vasculature, pleural space, and chest wall, and from technical factors such as patient rotation. Imaging plays a major role in establishing diagnoses and in appropriately guiding patient management, especially because some causes of unilateral hyperlucent hemithorax may be life threatening. The objective of this article is to review pediatric conditions that cause a unilateral hyperlucent hemithorax, with emphasis on their imaging findings.