We report the case of a patient with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) who exhibited sudden progression of lung infiltration while maintaining stable kidney function. The 69-year-old man was diagnosed with AAV and renal insufficiency 4 years ago. Pulmonic affectation was detected in the right lower lobe of lung by a computed tomography (CT) scan. After beginning cyclophosphamide pulse therapy and sequential therapy with low-dose prednisone, he underwent a 4-year follow-up to detect changes in hemoglobin levels and serum creatinine levels, and had chest CT examinations. The CT scan and creatinine assay showed stable pulmonic fibrosis and kidney function. Although there was no increase of creatinine and detectable perinuclear ANCA, the patient suffered a pulmonary hemorrhage and levels of hemoglobin became progressive lower; the lung infiltration was found to be enlarged compared to the last examination the previous year. After immunosuppressive therapy for one week, the lung fibrosis was progressive, increased pulmonary hemorrhage occurred, and the patient died due to respiratory failure but not end-stage renal failure.