OBJECTIVES: The purpose of this analysis is to examine hospital-based utilization in Wegener’s granulomatosis (WG), a form of autoimmune disease characterized by necrotizing granulomas and vasculitis affecting approximately 3 out of every 100,000 people in the US. METHODS: A retrospective cross-sectional analysis examined inpatient (N=7,202) and outpatient visits (N=24,971) in the MedAssets health system data from 2009 to 2013.  In addition to patient and hospital characteristics, the Charlson comorbidity index and its individual comorbidities were evaluated.  Analysis of prevalent procedures and their comparative effects on utilization were explored.  Measures of utilization included number of visits and length of stay (LOS). Negative-binomial multivariate regression was used to identify significant LOS drivers. RESULTS: Hospital utilization was primarily for outpatient services (77.6%) with a mean of 2.5 outpatient visits per patient. The primary diagnosis was WG for 58.6% of outpatients and16.6% of inpatients.  Other common inpatient diagnoses included pneumonia (5.2%), septicemia (3.5%), and acute renal failure (3.4%).  The sample included more females (54.6%) than males (45.3%) and 56.8% was between 40 and 69 years old. The mean Charlson score was 2.11 with renal disease (37.4%), chronic pulmonary disease (27.2%), diabetes (18.9%), congestive heart failure (11.1%), and rheumatic disease (10%) as the most prevalent comorbidities.  The most common inpatient procedures were hemodialysis (26.3%), packed cell transfusions (18.0%), closed bronchial biopsy (8.1%), and closed renal biopsy (6.5%).  Average LOS was 8.4 days.  The most significant drivers associated with longer LOS included bronchial (IRR=1.72, p<.0001) and renal (IRR=1.48, p<.0001) biopsy procedures, packed cell transfusions (IRR=1.41 ,p<.0001), and therapeutic plasmapheresis (IRR=1.34 ,p<.0001). CONCLUSIONS: Although a rare disease WG patients consume significant amounts of healthcare resources in the hospital setting. Primary utilization occurs in the outpatient setting, however, when  hospitalized LOS is often lengthy.  Further research is required to understand the effect of interventions/treatments on mitigating progress of this disease.