We report the pulmonary pathologic features in 87 open lung biopsies from 67 patients with Wegener's granulo-matosis (WG) who were treated at a single institution from 1968 to 1990. At the time of open lung biopsy, 48 patients (72%) had classical WG with renal involvement; 19 (28%) had limited WG without renal involvement. The pathologic features were divided into major and minor manifestations. In the 82 specimens demonstrating no infectious organism, the three major pathologic manifestations of classical WG observed were also useful diagnostic criteria and included: (a) parenchymal necrosis, (b) vasculitis, and (c) granulomatous inflammation accompanied by an inflammatory infiltrate composed of a mixture of neutrophils, lymphocytes, plasma cells, histiocytes, and eosinophils. Parenchymal necrosis was found in 84% of biopsy specimens either as neutrophilic microabscesses (65% of specimens) or as large (67%) or small (69%) areas of geographic necrosis. Areas of geographic necrosis were usually surrounded by palisading histiocytes and giant cells. Additional granulomatous lesions consisted of microabscesses surrounded by giant cells (69%), poorly formed granulomas (59%), and scattered giant cells (79%). Sarcoid-like granulomas were uncommon (4%), and in only one specimen (1%) appeared within an inflammatory lesion of WG. Vascular changes were identified in 94% of biopsy specimens. Vascular inflammation was classified as chronic (37% arterial, 64% venous), acute (37% arterial, 29% venous), nonnecrotizing granulomatous (22% arterial, 9% venous), and necrotizing granulomatous (22% arterial, 10% venous). Fibrinoid necrosis was relatively uncommon (11% arterial, 6% venous). Cicatricial changes were found in arteries in 41% of biopsy specimens and in veins in 16%. Capillaritis was present in 31% of specimens. Minor pathologic lesions were commonly observed in biopsy specimens associated with classical WG lesions, but they were usually inconspicuous and not useful diagnostic criteria. These included interstitial fibrosis (26%), alveolar hemorrhage (49%), tissue eosinophils (100%), organizing intraluminal fibrosis (70%), endogenous lipoid pneumonia (59%), lymphoid aggregates (37%), and a variety of bronchial/bronchiolar lesions including acute and chronic bronchiolitis (51% and 64%), follicular bronchiolitis (28%), and bronchiolitis obliterans (31%). These minor lesions were often found at the periphery of typical nodules of WG. However, in 15 specimens (18%) a minor pathologic feature represented the dominant or major finding: pulmonary fibrosis (six specimens, 7%), diffuse pulmonary hemorrhage (six specimens, 7%), lipoid pneumonia (one specimen, 1%), acute bronchopneumonia (one specimen, 1%), and chronic bronchiolitis, bronchiolitic obliterans with organizing pneumonia (BOOP), and bronchocentric granulomatosis (one specimen, 1%). Bronchial stenosis was found in three specimens (4%). In 10 specimens (12%) active vasculitis affecting veins or arteries could not be identified. Diffuse pulmonary hemorrhage associated with capillaritis was the primary finding in three of these specimens. Nodular interstitial fibrosis was the primary finding in six cases, and in three of these specimens cicatricial vascular changes were also present. In the 10th specimen, geographic necrosis, microabscesses, and scattered giant cells were present. This review illustrates the wide variation and broad spectrum of pathologic features that can occur in pulmonary WG and addresses the complicated differential diagnosis that can be encountered in the lung.