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Introduction: Patients with antineutrophil cytoplasmic antibody (ANCA)–associated vasculitis and idiopathic interstitial lung diseases (IIPs) are positive for myeloperoxidase (MPO)–ANCA. MPO–ANCA-positive vasculitis mainly comprises microscopic polyangiitis (MPA) and unclassifiable vasculitis. These diseases are frequently complicated by interstitial lung disease (ILD). Few studies have reported the clinical differences between the subtypes of MPO–ANCA-positive ILD. Therefore, this study aimed to examine the clinical findings and courses of MPO–ANCA-positive ILD. Method: This retrospective study enrolled 100 patients with MPO–ANCA-positive ILD who were categorized into three groups: MPA (n = 44), unclassifiable vasculitis (n = 29), and IIP (n = 27). Our study compared the clinical findings and prognosis of these patients and analyzed the poor prognostic factors. Furthermore, we assessed the association between the patients with and without acute exacerbation of ILD (AE-ILD). Results: Our study found clinical differences in serum markers, clinical symptoms, and treatment regimens among the three groups. ILD complications, as the main cause of death, differed among the three groups (P = 0.04). Patients with unclassifiable vasculitis showed higher survival rates than those with IIP (P = 0.046). Patients with AE-ILD showed fewer general symptoms (P = 0.02) and lower survival rates (P < 0.01) than those without AE-ILD. In multivariate analysis, AE-ILD development was a strong poor prognostic factor for MPO–ANCA-positive ILD. Conclusions: The subtypes of MPO–ANCA-positive ILD have different clinical features and prognoses. Patients who develop AE-ILD require careful evaluation of clinical courses. Key Points • In myeloperoxidase (MPO)–antineutrophil cytoplasmic antibody (ANCA)–positive interstitial lung disease (ILD), patients with unclassifiable vasculitis showed a better prognosis than those with idiopathic ILD.. • Development of acute exacerbation in ILD was a strong poor prognostic factor in patients with MPO–ANCA-positive ILD.. [ABSTRACT FROM AUTHOR]