Cystic lung diseases represent a broad set of disorders with different causes, but all of them are characterized by multiple thin-walled parenchymal lesions. Multidetector CT (MDCT), especially high-resolution CT (HRCT), is the imaging modality of choice for the diagnosis and follow-up of these entities. Cavities and emphysema are the most common alternative diagnoses that must be differentiated from true pulmonary cysts. In this review, we discuss the most common cystic lung diseases, their physiopathology, and the CT imaging appearance, with special emphasis on the key imaging findings that are crucial in their differential diagnosis.