This review deals with the diagnosis and treatment of idiopathic eosinophilic lung diseases. The term ‘eosinophilic lung diseases’ refers to a number of heterogeneous diseases which share the presence of eosinophilic infiltrates in the pulmonary parenchyma and increased numbers of eosinophils in the bronchoalveolar lavage (BAL), and which may or may not be accompanied by peripheral eosinophilia (PE). The clinical symptomatology of these diseases can vary from mild to severe and potentially fatal. As most patients with eosinophilic lung disease can be treated effectively, detailed symptom assessment and correct diagnosis are of crucial importance. Pneumon 2008; 21(2):156–166