The association of pulmonary fibrosis (PF) with myeloperoxidase antineutrophil cytoplasmic antibody (MPO-ANCA)-associated vasculitides has not been well documented. The aim of this study was to assess the clinicopathological characteristics of PF in patients who tested positive for MPO-ANCA. In this study, 31 patients (17 males and 14 females; mean age, 69 years) diagnosed as having PF with positive MPO-ANCA levels ranging from 10 to 840 EU with a mean of 112.5 EU, were evaluated clinicopathologically. Among 31 patients with PF, 22 had underlying systemic diseases such as collagen vascular diseases, while nine had unknown aetiology. Evidence of glomerulonephritis was demonstrated in 14 patients. The clinical features were a history of dry cough and/or fine crackles in all 31 patients. Chest CT scans showed honeycombing in the lung bases in 26 patients. The histopathological features of the diseased lung tissues in all 11 autopsied cases were compatible with the usual interstitial pneumonia (UIP) pattern. Vasculitis was confirmed in bronchial arteries and/or pulmonary arterioles in five patients. The mortality was as high as 13 of the 31 patients. The causes of death were: deterioration of PF in five (two of whom were associated with pulmonary haemorrhage), lung cancer in two, pneumonia in four, and digestive tract bleeding in two. The survival rates in PF with MPO-ANCA-negative collagen vascular diseases, cryptogenic fibrosing alveolitis (CFA), and PF with positive MPO-ANCA, were compared. The 5-year survival rate in PF with positive MPO-ANCA was worse than in PF with MPO-ANCA-negative collagen vascular diseases and was the same for CFA. Although there was no correlation between MPO-ANCA titres and the activity of PF, this study demonstrated that the presence of positive MPO-ANCA was an unfavorable prognostic factor in patients with PF.