A variety of pulmonary diseases have diffuse cystic abnormalities within the lungs, including emphysema, cystic bronchiectasis, desquamative interstitial pneumonia, lymphocytic interstitial pneumonia, usual interstitial pneumonia, lymphangioleiomyomatosis, Langerhans histiocytosis, cystic metastasis, Wegener granulomatosis, pneumocystis carinii pneumonia, pulmonary paragonimiasis, and septic pulmonary emboli. CT can easily detect cyctic abnormalities as common features in many diseases. However, some characteristic pattern of them can facilitate specific diagnoses.