OBJECTIVES: Atypical hemolytic uremic syndrome (aHUS) is a rare genetic disease affecting kidney function that predominantly affects children.  The objective of this study was to evaluate hospital-based utilization in patients with aHUS. METHODS: A retrospective cross-sectional study was conducted on 6571 aHUS discharges in the MedAssets health system data for inpatient (IP) and outpatient (OP) visits for the January 2009 to December 2013 timeframe. Age and gender, hospital characteristics, clinical comorbidities and measures of utilization including number of visits and length of stay (LOS) were described. Multivariable regression was used to identify significant drivers of hospital-based utilization. RESULTS: The sample included 2089 patients with more than 76.0% of the hospital visits occurring in the outpatient setting. The mean age of the sample was 23 years with 59.3% under the age of 18 and 61.0% female.  More than 60% of the visits occurred in teaching facilities and facilities with 300 beds or more. Among inpatient admissions, the average LOS was 16.02 days with the most common procedures being packed cell transfusions (41.7%) therapeutic plasmapheresis (29.8%) and serum transfusion (17.4%). Same-hospital readmissions occurred in 14.5% of the inpatient sample.  Comorbidities for this population included renal disease (56.2%), congestive heart failure (11.1%), chronic pulmonary disease (10.0%) and diabetes without chronic complications (8.0%).  Cardiovascular disease (2.8 days, p<.001), rheumatic disease (2.5 days, p<.05), and malignancy (4.2 days, p<.0001) were significantly associated with longer inpatient LOS. CONCLUSIONS: Patients with aHUS consume a significant amount of healthcare resources. Further research is required to understand the effect of interventions/treatments on mitigating the progress of this disease.