Objective. To compare the rate of severe infections after the onset of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) with the rate in the background population, and to identify predictors of severe infections among patients with AAV. Methods. The study cohort was 186 patients with AAV diagnosed from 1998 to 2010, consisting of all known cases in a defined population in southern Sweden. For each patient, 4 age-and sex-matched reference subjects were randomly chosen from the background population. Using the Skane Healthcare Register, all International Classification of Diseases codes of infections assigned from 1998 to 2011 were identified. Severe infections were defined as infectious episodes requiring hospitalization. Rate ratios were calculated by dividing the rate in AAV by the rate among the reference subjects. Results. The rate ratio for all severe infections was 4.53 (95% CI 3.39-6.00). The highest rate ratios were found for upper respiratory tract: 8.88 (3.54-25.9), Clostridium difficile: 5.35 (1.54-23.8), nonspecific septicemia 4.55 (1.60-13.8), and skin 5.35 (1.69-19.8). Of the severe infections, 38.4% occurred within 6 months of diagnosis, 30.2% from 7-24 months, and 31.4% after 24 months. High serum creatinine and older age at diagnosis were associated with severe infection (p amp;lt; 0.001). Of those with severe infection, 46.5% died during followup compared to 26% of patients without severe infection (p = 0.004). Conclusion. Patients with AAV have markedly higher rates of severe infection compared with the background population, especially patients with older age and impaired renal function. The risk of severe infection is particularly high in the first 6 months following the diagnosis of vasculitis.