BACKGROUND The outcomes of patients admitted to the intensive care unit (ICU) for acute manifestation of small-vessel vasculitis are poorly reported. The aim of the present study was to determine the mortality rate and prognostic factors of patients admitted to the ICU for acute small-vessel vasculitis. METHODS This retrospective, multicenter study was conducted from January 2001 to December 2014 in 20 ICUs in France. Patients were identified from computerized registers of each hospital using the International Classification of Diseases, Ninth Revision (ICD-9). Inclusion criteria were (1) known or highly suspected granulomatosis with polyangiitis, eosinophilic granulomatosis with polyangiitis, microscopic polyangiitis (respectively, ICD-9 codes M31.3, M30.1, and M31.7), or anti-glomerular basement membrane antibody disease (ICD-9 codes N08.5X-005 or M31.0+); (2) admission to the ICU for the management of an acute manifestation of vasculitis; and (3) administration of a cyclophosphamide pulse in the ICU or within 48 h before admission to the ICU. The primary endpoint was assessment of mortality rate 90 days after admission to the ICU. RESULTS Eighty-two patients at 20 centers were included, 94% of whom had a recent (<6 months) diagnosis of small-vessel vasculitis. Forty-four patients (54%) had granulomatosis with polyangiitis. The main reasons for admission were respiratory failure (34%) and pulmonary-renal syndrome (33%). Mechanical ventilation was required in 51% of patients, catecholamines in 31%, and renal replacement therapy in 71%. Overall mortality at 90 days was 18% and the mortality in ICU was 16 %. The main causes of death in the ICU were disease flare in 69% and infection in 31%. In univariable analysis, relevant factors associated with death in nonsurvivors compared with survivors were Simplified Acute Physiology Score II (median [interquartile range] 51 [38-82] vs. 36 [27-42], p = 0.005), age (67 years [62-74] vs. 58 years [40-68], p < 0.003), Sequential Organ Failure Assessment score on the day of cyclophosphamide administration (11 [6-12] vs. 6 [3-7], p = 0.0004), and delayed administration of cyclophosphamide (5 days [3-14] vs. 2 days [1-5], p = 0.0053). CONCLUSIONS Patients admitted to the ICU for management of acute small-vessel vasculitis benefit from early, aggressive intensive care treatment, associated with an 18% death rate at 90 days.