First described in 1951 as an allergic and granulomatous angiitis, Churg-Strauss syndrome (CSS) is a small-vessel vasculitis. Mean age at the time of diagnosis is approximately 50 years, with a sex ratio around 1. Asthma is the central feature of CSS and precedes the systemic manifestations in almost all cases, whereas 70% of the patients have maxillary sinusitis, allergic rhinitis, and/or sinus polyposis. General symptoms are frequent, and associated with pulmonary infiltrates in 38 to 77% of the patients; peripheral neuropathy, usually mononeuritis multiplex, in 64 to 75%; skin involvement in 40 to 70%; and gastrointestinal tract symptoms in 37 to 62%. Cardiac involvement is common, with pericarditis in 23% of the patients and myocarditis in 13%, and represents the primary cause of mortality. Hypereosinophilia is the main biological feature of CSS, whereas antineutrophil cytoplasm antibodies (ANCA), especially anti-myeloperoxidase (MPO), are found in one third to one half of the patients. Triggering factors, such as vaccination, desensitization, or exposure to leukotriene-receptor antagonists, have been suspected as contributing to the development of CSS, but its etiology has not yet been fully elucidated. T-helper type 2 (Th2) lymphocytes, by analogy with the pathogenesis of asthma, eosinophils infiltrating tissues, and anti-MPO ANCA are probably implicated in the pathogenesis of vasculitic lesions. CSS usually responds rapidly to corticosteroids. Adjunction of cyclophosphamide is indicated when at least one factor of poor prognosis is present. With treatment, remission is obtained in more than 80% of the patients, but it is often impossible to withdraw corticosteroids completely because of residual asthma. Relapses occur in 25% of the patients, half during the first year. The 10-year survival rate was 79% for our patients, with 73% of them requiring low-dose prednisone maintenance therapy for persistent asthma.