OBJECTIVES: To examine the comorbidities and economic burden of patients diagnosed with multiple sclerosis (MS) in the U.S. veteran population. METHODS:   The study sample was extracted from the Veterans Health Administration (VHA) Medical SAS datasets from October 1, 2005 through May 31, 2012. All patients diagnosed with MS throughout the study period were identified using International Classification of Diseases 9th Revision Clinical Modification (ICD-9-CM) diagnosis code 340.xx. Comorbid conditions were assessed for the 1-year baseline period before the MS identification date, and health care utilization and costs were assessed for 1 year of follow-up after the identification date. Statistical analyses were performed using SAS v9.3 software. RESULTS: There were 9,798 MS patients from 2005 to 2012 in the U.S. veteran population. The most frequent comorbidity for MS patients was hypertension (15.04%). All other comorbidities, including among others diabetes, depressive disorder, and lumbago, had frequencies of less than 10%. Common treatment medications for MS were simvastatin, omeprazole, lisinopril, and gabapentin.  A total of 9,724 (99.24%) MS patients had outpatient visits, while 8,471 (86.46%) patients had pharmacy visits and 1,976 (20.17%) inpatient visits. Outpatient, pharmacy and inpatient costs were $11,349 (standard deviation [SD]=$19,068), $3,220 (SD=$7,285), and $9,171 (SD=$57,129), respectively. CONCLUSIONS: MS treatment is complicated by the presence of comorbidities. Further analysis in the context of complicated comorbid condition diagnoses is required to improve the overall burden of illness of MS patients.