OBJECTIVES Because limited data are available on changes in direct costs (medical and prescription) and likelihood of health service utilization among employees treated with Interferon (IFN) â1a-IM for MS, the study aimed to assess the changes in direct costs and likelihood of health service utilization for persons with multiple sclerosis (MS) treated with IFN â1a-IM. METHODS A health care claims database of US employees from 2001-2008 was used to identify patients with MS (2 IFN â1a-IM prescriptions [Rxs] or an IFN â1a-IM Rx + MS diagnosis [ICD-9=340.X]). Employees with eligibility 6 months before and after their initial IFN â1a-IM Rx and no other disease-modifying therapies were included in the analysis. Non-parametric tests and t-tests were used to compare the mean and median direct medical costs and the likelihood of health service utilization before and after initiation of IFN â1a-IM. RESULTS Data from 68 employees with MS that took IFN â1a-IM (42 employees with health service utilization data) were eligible for analysis. All direct medical cost changes were significant (P<0.01). Mean medical costs decreased by $2872 (54%) from $5339 to $2467 and median costs decreased by $3691 (80%) from $4596 to $905. Significant (P<0.05) decreases in the likelihood of health service utilization were noted for the following: 11.9% for emergency department from 11.9% to 0%, 23.8% for outpatient hospital from 64.3% to 40.5%, and 16.7% for “other” (including home-care, ambulance, mobile unit, and unknown) from 31.0% to 14.3%. Inpatient hospital care decreased non-significantly (P=0.096) by 11.9% from 16.7% to 4.8%, while lab and office claims stayed the same (7.1% and 92.9%, respectively). CONCLUSIONS Direct medical costs decreased for IFN â1a-IM patients after therapy initiation, with reduced use of emergency department, inpatient and outpatient hospital care, and other services. These differences suggest the costs of Interferon â1a-IM are partially offset by medical care saving.