Churg-Strauss syndrome is a systemic ANCA-associated vasculitis arising almost exclusively in patients with a pre-existent asthma. Common clinical manifestations are marked blood eosinophilia, asthma, chronic sinusitis, cardiomyopathy, pulmonary infiltrates, gastrointestinal complaints and a multiplex neuropathy. The morphological substrate is an eosinophilic necrotizing vasculitis. Other eosinophilic disorders such as parasitic diseases, allergies and idiopathic hyper-eosinophilic syndrome have to be excluded. The mainstay of therapy is high-dose corticosteroids with the addition of cytotoxic drugs in patients with poor prognosis.