Allergic granulomatosis is a rare life-threatening systemic disorder of unknown origin, which represents a variant of systemic necrotizing vasculitis affecting medium-sized arteries and venules. Histologically, allergic granulomatosis is characterized by vascular and extravascular necrotizing palisading granulomas with prominent eosinophilia (Churg-Strauss granulomas). The clinical criteria include atopy with severe allergic asthma, pronounced peripheral eosinophilia, and nodular infiltrates of the skin and internal organs (Churg-Strauss granulomas). The internal organs most commonly involved are the lungs, gastrointestinal tract and, less often, the peripheral nerves, heart, and kidneys. Associated symptoms include fever, arthralgias and skin rashes, such as erythema multiforme, necrotizing venolitis, fixed drug eruption, and urticaria. Allergic granulomatosis shares common features with Wegener's granulomatosis and polyarteritis nodosa and may be related to the latter condition; overlap syndromes are a well-known occurrence. Similar to the other manifestations of systemic necrotizing vasculitis, immune complexes have been detected in fresh lesions and are suspected of being the basic pathogenetic findings. The causative antigens are likely to be respiratory antigens. The prognosis of untreated allergic granulomatosis is poor (mortality of approximately 50% within the first year). Systemic corticosteroids and cyclophosphamide are effective; complete remissions following cyclophosphamide treatment have been reported.