Anti-neutrophil cytoplasmic autoantibodies (ANCA) occur in a subset of patients with systemic small vessel vasculitis, including patients with Wegener's granulomatosis, microscopic polyangiitis (microscopic polyarteritis), and Churg-Strauss syndrome. Pulmonary disease appears at some time during the course in many patients with ANCA-associated vasculitis. The histologic features of 25 open lung biopsies and two autopsy cases were studied from 27 patients with ANCA. Patients' ages ranged from 8 to 79 years with a mean of 52.6 years. There were 12 females and 15 males. Autoantibodies were characterized as C-ANCA in 13 patients and as P-ANCA in 14 patients. Anti-proteinase 3 antibodies were documented in 12 of 13 patients with C-ANCA. Anti-myeloperoxidase antibodies were documented in all 14 patients with P-ANCA. Vascular lesions were present in 21 patients (78%) and 11 patients (41%) had bronchial lesions. Capillaritis was the most common vascular lesion (17 patients, 63%), and was found with similar frequency in patients with C-ANCA and those with P-ANCA. Extravascular structures were a common site of tissue injury. Airway lesions including bronchiolitis obliterans organizing pneumonia (4 patients, 19%), necrotizing granulomatous inflammation (4 patients, 15%), and non-granulomatous inflammation (3 patients, 11%) were more commonly associated with patients with C-ANCA. Interstitial lesions were found in 20 patients (74%), and included necrotizing granulomatous inflammation (8 patients, 30%), fibrosis (13 patients, 48%), and chronic inflammation (12 patients, 44%). No histologic lesion were found that were specific for C-ANCA or P-ANCA. This series demonstrates the wide variety of pulmonary lesions found in patients with ANCA-associated pulmonary disease, and shows that extravascular structures are a common site of injury in ANCA-associated vasculitis.