© 2018 Objective: Previous cost analyses have found small to negative margins between hospitalization cost and reimbursement for endovascular aneurysm repair (EVAR). Hospitals obtain reimbursement on the basis of Medicare Severity Diagnosis Related Group (MS-DRG) coding to distinguish patient encounters with or without major comorbidity or complication (MCC). This study's objective was to evaluate coding accuracy and its effect on hospital cost for patients undergoing EVAR. Methods: A retrospective, single university hospital review of all elective, infrarenal EVARs performed from 2010 to 2015 was completed. Index procedure hospitalizations were reviewed for MS-DRG classification, comorbidities, complications, length of stay (LOS), and hospitalization cost. Patients’ comorbidities and postoperative complications were tabulated to verify accuracy of MS-DRG classification. Misclassified patients were audited and reclassified as “standard” or “complex” on the basis of a corrected MS-DRG: standard for 238 (major cardiovascular procedure without MCC) and complex for 237 (major cardiovascular procedure with MCC). Results: There were 104 EVARs identified, including 91 standard (original MS-DRG 238, n = 85; MS-DRG 254, n = 6) and 13 complex hospitalizations (original MS-DRG 237, n = 9; MS-DRG 238, n = 3; MS-DRG 253, n = 1). On review, 3% (n = 3) of the originally assigned MS-DRG 238 patients were undercoded while actually meeting MCC criteria for a 237 designation. Hospitalizations coded with MS-DRG 253 and 254 were considered billing errors because MS-DRG 237 and 238 are more appropriate and specific classifications as major cardiovascular procedures. Overall, there was a 9.6% miscoding rate (n = 10), representing a total lost billing opportunity of $587,799. Mean LOS for standard and complex hospitalizations was 3.0 ± 1.5 days vs 7.8 ± 6.0 days (P <.001), with respective intensive care unit LOS of 0.4 ± 0.7 day vs 2.6 ± 3.1 days (P <.001). Postoperative complications occurred in 23% of patients; however, not all met the Centers for Medicare and Medicaid Services criteria as MCC. Miscoded complexity was found to be due to postoperative events in all patients rather than to missed comorbidities. Mean hospitalization cost for standard and complex patients was $28,833 ± $5597 vs $41,543 ± $12,943 (P <.001). Based on institutional reimbursement data, this translates to a mean loss of $5407 per correctly coded patient. Miscoded patients represent an additional overall reimbursement loss of $140,102. Conclusions: Our study reveals a large lost billing opportunity with miscoding of elective EVARs from 2010 to 2015, with errors in categorization of the procedure as well as miscoding of complexity. The revenue impact is potentially significant in this population, and additional reviews of coding practices should be considered.