Four cases that showed prior pulmonary fibrosis as well as subsequent RPGN and pulmonary hemorrhage were both MPO-ANCA- and anti-GBM Ab-positive at the time of RPGN. The glomeruli disclosed features compatible with anti-GBM Ab disease, but the clinical and pathological vasculitic manifestations, including prior pulmonary fibrosis that might be an early manifestation of ANCA disease, suggested the occurrence of MPO-ANCA-associated vasculitis. Furthermore, 1 case subsequently showed repetitive pulmonary hemorrhage with re-elevated MPO-ANCA positivity but without anti-GBM Ab positivity, and this event was possibly due to MPO-ANCA-associated alveolar capillaritis. As anti-GBM Ab disease is generally thought not to manifest the clinical and pathological features of vasculitis excluding the kidney, MPO-ANCA might be a key factor regarding the occurrence of this dual positive disease.