The presence of peripheral eosinophilia with lung infiltrates poses a diagnostic challenge for the clinician. The differential diagnosis includes a wide spectrum of diseases. In some of them (for example vasculitis, lymphoma) eosinophilic pneumonia represents just another "symptom" and not the final diagnosis. A thorough diagnostic procedure is required to examine all related clinical entities in order to establish a firm diagnosis. In particular, Idiopathic Chronic Eosinophilic Pneumonia (ICEP) is a rare disorder. In the majority of cases, it is characterized by peripheral eosinophilia, lung infiltrates, bronchoalveolar lavage eosinophilia (above 25%), exclusion of other possible causes and last but not least an impressive improvement under steroid therapy. Relapses are common but they do not seem to be related with ICEP associated mortality.