We report a case of idiopathic crescentic glomerulonephritis with pulmonary hemorrhage associated with anti-myeloperoxidase antibodies (anti-MPO ab). A 74 year-old female was admitted to our hospital because of rapidly progressive glomerulonephritic syndrome and dyspnea with bloody sputum. On admission anti-MPO ab, one of anti-neutrophil cytoplasmic antibodies, were detected but anti-GBM antibodies and immune complexes were not detected. Renal biopsy showed crescentic glomerulonephritis and lung biopsy showed massive alveolar hemorrhage. Both tissue had pauci-immune deposit by immunofluorescence microscopy. Hemodialysis and steroid administration were started. Pulmonary hemorrhage was improved remarkably, but renal failure progressed rapidly to end stage kidney, then hemodialysis was continued. Although subsequent 3 years uneventful maintenance hemodialysis had been performed, she admitted to our hospital again because of progressive dyspnea with hemoptysis after upper respiratory tract infection. On admission anti-MPO ab were detected again and steroid administration was started. Pulmonary hemorrhage was improved with decreased anti-MPO ab titer. While tapering the dosis of steroid, anti-MPO ab again increased and pulmonary hemorrhage recurred. Although pulse methylprednisolone therapy and plasma exchange were performed, respiratory failure progressed rapidly and she died of sepsis. Postmortem examination showed no evidence of systemic vasculitis. In this case, titer of anti-MPO ab was associated with not only idiopathic crescentic glomerulonephritis but also with pulmonary hemorrhage. We tried to detect enzymatically active MPO in serum. Titer of serum MPO was also associated with disease activity and anti-MPO ab. It is suggested that both anti-MPO ab and serum MPO are closely related to the pathogenesis of idiopathic crescentic glomerulonephritis and pulmonary hemorrhage.