OBJECTIVES: Treatment restrictions because of patient financial burden may have unintended consequence on management of multiple sclerosis (MS). The goal was to evaluate MS treatment compliance among patients enrolled in insurance plans with various cost-sharing arrangements for disease modifying therapies (DMT). METHODS: Thomson Reuters MarketScan® Commercial and Medicare databases (January 1, 2004-December 31, 2009) were used to identify adult patients with MS (ICD-9-CM: 340) and on DMT (claim for first DMT was the index event). Patients were assigned to three mutually exclusive cohorts based on DMT insurance plan cost-sharing levels: $0-, low- and high-cost-sharing. Median cost-sharing for DMTs, standardized to 2010 US dollars, was used to determine threshold between ‘low’ and ‘high’. Medication possession ratio (MPR) and persistence (time to discontinuation of DMT) were evaluated during 12-months following index. RESULTS: A total of 14,718 patients were identified and had cost-sharing arrangements as follows: $0 cost-sharing (n=1,361, 9.2%), low cost-sharing (n=6,044, 41.1%) and high cost-sharing (n=7,313, 49.7%). Majority were female (77%) and mean age was 46.1 years. Patients in $0 cost-sharing plans had significantly higher MPR values (0.83) than patients in both the low cost-sharing (0.81; p=0.037) and high cost-sharing plans (0.79; p<0.001). Discontinuation rates were also lower among patients in $0 cost-sharing plans (34.1%) versus patients with any cost-sharing (35.5% for low and 37.2% for high cost-sharing; p<0.001). CONCLUSIONS: Patients in plans with no cost-sharing have greater adherence and are less likely to discontinue treatment in the 12-month period following DMT initiation. These results suggest that patients with MS are sensitive to the financial costs associated with DMT and may make treatment decisions based on this burden. Manufacturer co-pay assistance programs designed to reduce patient financial burden were not considered in this analysis.  Therefore, these results may underestimate the effects of benefit design on medication adherence and persistence.