This large observational cohort of patients with ANCA-associated vasculitis suggests many findings and implications. The 77% remission rate was comparable with previously reported rates of 70% to 92% (5, 8, 21–23). Treatment resistance was most common among patients presenting with higher serum creatinine levels, greater disease chronicity, and vascular sclerosis on renal biopsy. In previous reports, cumulative organ damage (measured by the Vasculitis Damage Index) (24), glomerular sclerosis, interstitial infiltrates, tubular necrosis, atrophy (25), and other markers of chronic disease were consistently labeled as predictors of treatment resistance, despite differences in statistical models and outcome definitions. These associations were independent of the level of disease activity, disease category, ANCA pattern or specificity, and demographic region. In this cohort, vascular sclerosis on biopsy was also an independent predictor of treatment resistance. We concluded that this association possibly resulted from chronic renal damage secondary to hypertension or other atherosclerotic processes; ANCA-associated nephritis may have also been a contributing factor. The impact of renal damage as a predictor of resistance emphasizes the importance of early diagnosis and prompt institution of therapy.