Chronic eosinophilic pneumonia (CEP) is a disease of unknown cause. The hallmark of CEP is eosinophil accumulation in the lungs. While the triggering factor is unknown, eosinophil accumulation in the lungs is now believed to be secondary to the actions of eosinophil-specific chemoattractants, including eotaxin and regulated upon activation, normal T-cell expressed and secreted (RANTES), and IL-5 released from Th2 lymphocytes in the lungs. There is a female preponderance in CEP, with a peak incidence in the 5th decade; the onset is insidious with weight loss, cough, and dyspnea. An atopic history is common, but asthma is not a prerequisite for the development of CEP. Airways obstruction may develop during the course of CEP, but may also result from CEP. The chest x-ray usually shows bilateral peripheral shadows, which may be migratory. Peripheral eosinophilia is usual. Standard treatment of CEP is with oral steroids, usually with dramatic resolution of symptoms and radiographic changes; however, relapses are common when the daily steroid dose is reduced below 15 mg. Current data suggest that when treatment is stopped, relapse is common in the majority of patients (>80%) followed for a sufficiently long period of time. Some recent reports suggest that treatment with inhaled steroids may be of some value in this condition.