The natural course of as-yet-untreated ANCA-associated vasculitis (AAV) or complications of immunosuppressive treatment may result in rapid clinical deterioration with the need of admission to an intensive care unit (ICU). The aim of this retrospective study was to assess the outcome of patients with renal AAV admitted to the ICU in a single center. We reviewed the medical records of all 218 patients with AAV followed in our department between January 2001 and December 2006 and selected those admitted to the ICU. To assess the severity of critical illness, the Acute Physiology and Chronic Health Evaluation (APACHE II) and Sequential Organ Failure Assessment (SOFA) score on the first ICU day were calculated. Birmingham Vasculitis Activity Score (BVAS) was calculated to represent the total disease activity. Thirty patients with AAV (11 women, 19 men; mean age 61.5 +/- 13.2 years; 20 x cANCA, 10 x pANCA positive) were included. The most common reasons for ICU admission were as follows: active vasculitis (13 patients, 43.3 %), infections (7 patients, 23.3%), and other causes (10 patients, 33.3%). The in-ICU mortality was 33.3% (10 patients). The most common cause of death was septic shock (in 5 patients). The APACHE II (33.5 vs. 23.8) and SOFA scores (11.9 vs. 6.6), but not BVAS (11.5 vs. 16.1), were statistically significantly higher in non-survivors than in survivors (p < 0.01). In conclusion, the in-ICU mortality in AAV patients may be predicted by APACHE II and SOFA scores. While active vasculitis is the most frequent reason for ICU admission, the mortality rate is highest in patients with infectious complications.