Cystic lung disease is a group of pulmonary disorders characterized by the presence of multiple cysts that are defined as low-attenuation areas with thin walls (wall thickness usually less than 2 mm). Cysts are increasingly being recognized on HRCT of the thorax and always present a diagnostic dilemma. The common cystic lung diseases are lymphangioleiomyomatosis (LAM), pulmonary Langerhans cell histiocytosis (LCH), and Birt-Hogg-Dubé syndrome. There are two interstitial lung diseases that can present with multiple cysts, namely, desquamative interstitial pneumonia (DIP) and lymphocytic interstitial pneumonia (LIP). Multiple pulmonary cysts (pneumatoceles) can also be seen during the course of Pneumocystis carinii pneumonia (PCP), now known as Pneumocystis jirovecii pneumonia (PJP). There are two challenges in reporting the HRCT with cystic lung diseases: first to differentiate the true cysts from their mimickers and second to provide an accurate diagnosis of cystic lung disease. In most cases, diagnosis can be made by the characterization of the cysts and ancillary radiological findings coupled with a careful review of clinical information.