Antineutrophil cytoplasmic antibody (ANCA)-associated small-vessel vasculitides are major causes of rapidly progressive glomerulonephritis (RPGN). Although recent papers suggest differences in clinicoepidemiological manifestations of ANCA-associated vasculitis between Japan [microscopic polyangiitis (MPA) " Wegener's granulomatosis (WG)] and Europe (WG"MPA), little is known about the prevalence and serological pattern. We retrospectively analyzed 27 RPGN patients who were admitted in our hospital over the past 11 years and who could be basically followed for more than 1 year, concerning the incidence of ANCA-related vasculitis, the presence of (MPO)/proteinase 3 (PR3)-ANCA and their clinical outcomes. As there were no PR3-ANCA single positive and/or WG patients, all patients were serologically divided into four groups; Groups I: MPO-ANCA single-positive patients (N = 11), II: MPO-ANCA and PR3-ANCA double-positive patients (N = 3), III: antiglomerular basement membrane antibody (anti-GBM Ab)-positive patients (N = 6), and IV: all negative patients (N = 7). Patients in Groups II/III showed more severe manifestation at admission. However, in Group I, only 36.3% patients avoided death and/or dialysis-dependent end-stage renal disease. Most patients in Group IV were women (85.7%), and 50% of these patients was diagnosed as having rheumatic diseases. Every patient in Groups I-III was treated with oral corticosteroid and/or methylprednisolone pulse therapy. Most patients treated with immunosuppressants showed severe prognosis because of frequent recurrences of vasculitis and infectious episodes after repeated and prolonged treatments with immunosuppressants. Present analysis further confirms the epidemiological and serological differences in ANCA-related RPGN between Japan and Europe, and reinforced the fact that ANCA-associated vasculitis is the most serious causal disease for RPGN.