In 1936, and again in 1939, Wegener (26, 27) reported a syndrome which has aroused widespread interest among clinicians, pathologists, and, more recently, radiologists. His 3 cases, which he designated rhinogenous granuloma, presented a severe destructive granulomatous rhinitis associated with ulcerations in the upper respiratory tract. Pulmonary and renal involvement were also prominent features. The illness terminated fatally within seven months after onset of symptoms. Pathologically, the condition was characterized by the presence of a peculiar necrotizing granulomatous process in the upper respiratory tract and sometimes in the lungs, focal glomerulonephritis, and a more or less generalized angiitis which in many respects resembled periarteritis nodosa. Similar cases had been reported earlier by Klinger (15) and by Rössle (22). Ringertz (19) subsequently reported a case with pulmonary involvement but without nasal or upper respiratory lesions. The nasal and facial manifestations of Wegener's cases were similar to those of a condition which had been recognized for many years and reported under various names, including lethal granuloma of the midline facial structures, granuloma gangraenescens, and malignant granuloma (4). Although Wegener maintained that the histologic appearance of the rhinogenous granuloma in his cases differed from that of lethal granuloma, others have considered the two diseases closely related and have suggested that lethal granuloma constitutes the localized form of Wegener's syndrome (11, 12). In 1951, Churg and Strauss (5) reported a group of cases with severe asthma, fever, and eosinophilia, in which necrotizing angiitis and extravascular granulomas were present. Recurrent episodes of pneumonia and a variety of cutaneous lesions were additional features of the disease, which they called allergic angiitis and granulomatosis. The close similarity to Wegener's syndrome was soon recognized (10, 12). Thus, there exists a group of diseases bearing an unmistakable resemblance to one another, particularly in regard to the presence of granulomas and angiitis, yet showing distinct differences. First, there is Wegener's granulomatosis, with the triad of granulomatous lesions with necrosis in the upper air passages and/or lower respiratory tract, widespread vasculitis, and granulomatous necrotizing glomerulitis. Next, there is lethal granuloma with similar facial and upper respiratory lesions, but frequently without pulmonary, renal, and vascular components. Finally, there is Churg and Strauss' granulomatosis, which presents many of the characteristics of Wegener's syndrome but differs from it in histologic details (to be discussed later) and in the prominence of the clinical stigmata of allergy (12). Many cases of Wegener's syndrome, lethal granuloma, and allergic angiitis and granulomatosis do not present the gamut of features usually described in the literature.