Several lines of evidence suggest that CSS is not simply the coincidental development of vasculitis in patients with asthma. The asthma seen in CSS is notable for being of late onset; it is frequently severe and is associated with a greater degree of eosinophilia than is typically seen in bronchial asthma. There is often no personal or family history of atopic disease (2). In addition, cases are well described in which the asthma develops shortly before or simultaneously with vasculitis (3,4). The recognition of CSS as a separate disease entity is important, because its distinctive natural history (2,5), its frequent rapid response to treatment, and its good overall prognosis (4) suggest pathogenic mechanisms that differ either in nature or in degree compared with other forms of necrotizing vasculitis.