In this retrospective study, we analyzed 17 patients presenting with pulmonary fibrosis and a positive ANCA testing. This group was compared with a control group of 12 patients with IPF and negative ANCA testing. Patients were 15 males and 2 females, with a mean age of 66 years. Eight patients were past smokers, 3 current smokers and 6 non-smokers. Lung function tests at diagnosis were as follows (% predicted): total lung capacity 73%+/-18, vital capacity 82%+/-23, forced expiratory volume in 1 s (FEV(1)) 88%+/-24, carbon monoxide diffusion capacity of the lung 49%+/-2 (% predicted). Bronchoalveolar lavage results showed an increased cellularity with increased neutrophils counts. High resolution computed tomography of the chest showed prominent fibrosis with some degree of ground-glass attenuation in all patients. These characteristics were similar to the control group. Microscopic polyangiitis (MPA) was a major complicating event in ANCA-positive patients, occurring in 7 patients (anti-myeloperoxidase specificity in 5 patients). Pulmonary fibrosis predated occurrence of MPA in 6 patients and was diagnosed concomitantly with MPA in 1 patient. During the follow-up, 10/17 patients died. The death was directly related to vasculitis in 3 patients. We conclude that patients with pulmonary fibrosis should be evaluated for the presence of ANCA. Patients with positive ANCA testing, particularly if anti-myeloperoxidase, should be carefully monitored to detect the occurrence of microscopic polyangiitis.