A 68-year-old woman was hospitalized for evaluation of progressive dyspnea, cough, and hemoptysis. She had a 2-month history of malaise, anorexia, arthralgias, and a 30-lb weight loss. Symptoms did not improve with outpatient antibiotic therapy. Laboratory studies were significant for profound anemia, elevated erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and decreased renal function. Perinuclear-pattern antineutrophil cytoplasmic antibody (p-ANCA) and myeloperoxidase (MPO) antibody were positive. Urinalysis showed microscopic hematuria with granular and red blood cell casts. Chest radiograph revealed bilateral alveolar infiltrates (Figure 79-1). Bronchoscopy with bronchoalveolar lavage was consistent with alveolar hemorrhage, and transbronchial lung biopsy showed changes of pulmonary capillaritis (Figure 79-2). An extensive infectious workup was negative. A diagnosis of microscopic polyangiitis (MPA) was made. The patient was treated with high-dose corticosteroids and oral cyclophosphamide, resulting in gradual clinical improvement. She was subsequently switched to azathioprine for maintenance of remission.