Lung involvement in Crohn's disease is not well characterized. We reviewed our experience with 11 lung biopsies (seven wedge and four transbronchial) from patients with Crohn's disease to study this association further. Negative cultures, special stains for organisms Gomori-methenamine-silver [GMS], acid fast), and polymerase chain reaction for (four cases) were required for inclusion. The group included five women and six men with a mean age of 47 years (range 13-84 years). A diagnosis of Crohn's disease preceded the lung disease in nine patients. In two patients the diagnosis of Crohn's disease followed the diagnosis of their pulmonary disease 1 and 15 months later. Radiologically, eight patients had diffuse infiltrates, two had bilateral nodular infiltrates, and one had a mass. Chronic bronchiolitis with nonnecrotizing granulomatous inflammation was present in four patients, one of whom was taking mesalamine. Two patients had an acute bronchiolitis associated with a neutrophil-rich bronchopneumonia with suppuration and vague granulomatous features. One patient on mesalamine had cellular interstitial pneumonia with rare giant cells. Four patients demonstrated organizing pneumonia with focal granulomatous features, two of whom were taking mesalamine, and one of these two responded to infliximab (anti-tumor necrosis factor) monoclonal antibody therapy. Noninfectious pulmonary disease in patients with Crohn's disease has variable histologic appearances, including granulomatous inflammation and airway-centered disease resembling that seen in patients with ulcerative colitis. Drugs may contribute to pulmonary disease in some patients.