Churg-Strauss syndrome (CSS) is a systemic vasculitis characterized by the presence of asthma, hypereosinophilia, and necrotizing vasculitis with extravascular eosinophil granulomas. In this retrospective study of 96 patients between 1963 and 1995, we analyzed clinical manifestations, identified prognostic factors, and assessed the long-term outcome. CSS was diagnosed when asthma, hypereosinophilia > 1,500/mm3 or > 10%, and clinical manifestations consistent with systemic vasculitis, with or without histologic evidence, were present. Asthma was the most frequently observed manifestation at presentation, with mononeuritis multiplex the second. Other common manifestations were weight loss, fever, myalgia, skin involvement, paranasal sinusitis, arthralgia, pulmonary infiltrate, and gastrointestinal involvement. Mean eosinophilia at presentation was 7.193 +/- 6.706/mm3; ANCA, present in 20 of 42 (47.6%) patients, predominantly gave the perinuclear labeling pattern. All the patients were treated with corticosteroids alone or in combination with cyclophosphamide or plasma exchanges. Clinical remission was obtained in 91.5%; 22 (25.6%) patients relapsed. Twenty-three patients died during follow-up: 11 of these deaths were directly due to vasculitis. The presence of severe gastrointestinal tract or myocardial involvement was significantly associated with a poor clinical outcome. The long-term prognosis of CSS is good and does not differ from that of polyarteritis nodosa, although most patients need low doses of oral corticosteroids for persistent asthma, even many years after clinical recovery from vasculitis.