Idiopathic chronic eosinophilic pneumonia (ICEP) is characterized by subacute or chronic respiratory and general symptoms, alveolar and/or blood eosinophilia, and peripheral pulmonary infiltrates on chest imaging. Eosinophilia is present in most cases, usually in excess of 1000/mm3. In absence of significant blood eosinophilia, a diagnosis of ICEP is supported by the demonstration of bronchoalveolar lavage eosinophilia. ICEP is typically associated with eosinophil counts higher than lymphocyte counts in the bronchoalveolar lavage. ICEP is a rare disorder of unknown cause. Its exact prevalence remains unknown. ICEP may affect every age group but is rare in childhood. It is twice as frequent in women as in men. One third to one half of the ICEP patients have a history of asthma. The mainstay of treatment of ICEP is systemic corticosteroids. Response to oral corticosteroid therapy is dramatic and has led to the consideration of corticosteroid challenge as a diagnostic test for ICEP. Nevertheless, relapses or development of severe asthma are frequent when tapering or withdrawing treatment. Long-term oral corticosteroid therapy is necessary in up to half of the patients.