Immunosuppressive therapy and clinical evolution were studied in 49 patients (29 females) with antineutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis. The mean age of patients at presentation was 55 years, and the mean (+/-SD) follow-up was 43 months (+/-33) (range, 3-140). Among the 49 patients, 10 had biopsy-proven Wegener's granulomatosis, 33 microscopic polyangiitis, 2 Churg-Strauss syndrome, and 4 idiopathic crescentic glomerulonephritis. IgG ANCA autoantibodies were detected in all patients. Induction therapy included pulses and oral administration of methylprednisolone (MP) with oral administration of cyclophosphamide (CP) and plasma exchange in patients with alveolar hemorrhage and serum creatinine (SCr) levels >/= 6 mg/dL. CP was converted to azathioprine (AZA) or mycophenolate mofetil (MMF) after 3-6 months of therapy. Low doses of MP with or without AZA or MMF were administered until the end of follow-up. Therapy institution resulted in remission of disease in all patients. The mean SCr levels decreased from 4.9 mg/dL (+/-2.5) at the onset of the disease to 2.8 mg/dL (+/-1.7) (P > 0.0001), and 3.2 mg/dL (+/-2.3) (P > 0.0001) after 3 and 6 months, respectively. At the end of follow-up, 17 (35%) patients progressed to end-stage renal disease after 34 months (+/-29) (range, 3-98), and 30 (61%) patients maintained sufficient renal function. Two patient deaths were attributed to immunosuppression. Patients with high SCr levels at diagnosis and severe interstitial fibrosis found in renal biopsy had poor renal outcome (P > 0.01 and P > 0.02, respectively). Induction therapy with MP and CP seems to be the regimen of choice in patients with ANCA-associated glomerulonephritis. Early diagnosis and therapy institution as well as long-term treatment lead to acceptable renal survival.