This study aimed to identify clinical and histologic prognostic indicators of renal outcome in patients with ANCA-associated vasculitis and severe renal involvement (serum creatinine >500 μmol/L). One hundred patients who were enrolled in an international, randomized, clinical trial to compare plasma exchange with intravenous methylprednisolone as an additional initial treatment were analyzed prospectively. Diagnostic renal biopsies were performed upon entry into the study. Thirty-nine histologic and nine clinical parameters were determined as candidate predictors of renal outcome. The end points were renal function at the time of diagnosis (GFR0) and 12 mo after diagnosis (GFR12), dialysis at entry and 12 mo after diagnosis, and death. Multivariate analyses were performed. Predictive of GFR0 were age (r = −0.40, P = 0.04), arteriosclerosis (r = −0.53, P = 0.01), segmental crescents (r = 0.35, P = 0.07), and eosinophilic infiltrate (r = −0.41, P = 0.04). Prognostic indicators for GFR12 were age (r = −0.32, P = 0.01), normal glomeruli (r = 0.24, P = 0.04), tubular atrophy (r = −0.28, P = 0.02), intraepithelial infiltrate (r = −0.26, P = 0.03), and GFR0 (r = 0.29, P = 0.01). Fibrous crescents (r = 0.22, P = 0.03) were predictive of dialysis at entry. Normal glomeruli (r = −0.30, P = 0.01) and treatment arm (r = −0.28, P = 0.02) were predictive of dialysis after 12 mo. No parameter predicted death. Both chronic and acute tubulointerstitial lesions predicted GFR12 in severe ANCA-associated glomerulonephritis, whereas plasma exchange was a positive predictor of dialysis independence after 12 mo for the entire patient group. Plasma exchange remained a positive predictor when patients who were dialysis dependent at presentation were analyzed separately (r = −0.36, P = 0.01). Normal glomeruli were a positive predictor of dialysis independence and improved renal function after 12 mo, indicating that the unaffected part of the kidney is vital in determining renal outcome.