The clinical and morphologic findings of allergic granulomatosis and angiitis of Churg and Strauss in 21 men and 9 women were reviewed. The classic features are those of systemic vasculitis in a setting of bronchial asthma and eosinophilia. Pathologically there is necrotizing vasculitis of small arteries and veins with extravascular granulomas, and infiltration of vessels and perivascular tissues with eosinophilia. These features differentiate it from poly-arteritis nodosa. The lungs, peripheral nerves, and skin are most frequently involved. Renal failure was encountered in only one patient in this series. Shortness of the interval from onset of asthma to appearance of vasculitis is an unfavorable prognostic sign. Corticosteroids seem to influence long-term survival favorably.