Clinical course of anti-neutrophil cytoplasmic autoantibody-associated glomerulonephritis and systemic vasculitis. The Glomerular Disease Collaborative Network OBJECTIVES: To determine the spectrum of clinical manifestations in patients with anti-neutrophil cytoplasmic autoantibody (ANCA)-associated glomerulonephritis; to determine renal and patient survival in these patients; to compare survival among patients treated with corticosteroids alone, corticosteroids plus intravenous cyclophosphamide or corticosteroids plus oral cyclophosphamide; and to assess the correlation of disease manifestations and treatment response with ANCA subtypes and serial autoantibody titers. DESIGN: Inception cohort study; mean follow-up of 24 months. SETTING: Collaborative network of 120 university and private practice nephrologists (The Glomerular Disease Collaborative Network). PARTICIPANTS: Seventy patients with ANCA and pauci-immune necrotizing and crescentic glomerulonephritis, of whom 59 were treated with either corticosteroids alone (14 patients), corticosteroids plus oral cyclophosphamide (30 patients), or corticosteroids plus intravenous cyclophosphamide (15 patients). MAIN RESULTS: Of the 70 patients, 18 had renal-limited disease (idiopathic crescentic glomerulonephritis); 15, nonpulmonary extrarenal disease consistent with polyarteritis nodosa; and 37, pulmonary disease consistent with Wegener granulomatosis or alveolar capillaritis. There were overlapping manifestations of disease between patients with autoantibodies producing a cytoplasmic pattern and patients with autoantibodies producing a perinuclear pattern; however, the perinuclear pattern occurred more frequently in patients with renal-limited disease. Renal and patient survival was 75% at 24 months, and no difference in survival was seen between patients with renal-limited disease and those with systemic disease. No differences in survival were seen between patients treated with oral cyclophosphamide and those treated with intravenous cyclophosphamide; however, the comparative data from patients treated with corticosteroids alone were inconclusive. In general, autoantibody titers correlated with response to treatment and disease activity, but there were exceptions. CONCLUSIONS: Patients with ANCA have various forms of necrotizing vascular inflammation, ranging from renal-limited disease to widespread systemic vasculitis, including polyarteritis nodosa and Wegener granulomatosis. Oral corticosteroids with either oral or intravenous cyclophosphamide appear to be equally effective therapy for ANCA-associated glomerulonephritis. 