OBJECTIVES: 1) Identify the prevalence of access barriers to prescription medications among beneficiaries with Multiple Sclerosis (MS); and 2) estimate the out of pocket price of commonly used prescription medications among insured and under-insured MS beneficiaries. METHODS: Using claims data from the Medicare Current Beneficiary Survey (MCBS) 1992-2001, we identified 156 beneficiaries with a diagnosis of multiple sclerosis on four or more claims (ICD-9 340). The MCBS is an overlapping panel survey linked to associate claims that includes questions on out-of-pocket price, access, and use of prescription medications. We estimated the average out-of-pocket price of prescription medications and prevalence of perceived economic barriers to address the hypothesis that the expansion of Medicare to include an outpatient drug benefit will decrease beneficiaries' burden of multiple sclerosis. RESULTS: Few MS beneficiaries (5%) reported that they did not get prescription medications that were prescribed for them. Some beneficiaries (15%) reported delaying health care due to the cost. The average out-of-pocket cost of commonly used medications (e.g., baclofen (Baclofen®), interferon beta-1B (Betaseron ®), and fluoxetine (Prozac ®)) among the insured is about half the price borne by the under-insured beneficiaries. For example, interferon beta-1B is $27 per prescription among insured beneficiaries, and $58.50 among under-insured beneficiaries. Similar results were found for other medications that are common among MS beneficiaries. CONCLUSIONS: Our findings suggest that MS beneficiaries perceive few economic barriers to necessary health care, particularly prescription medications. However, we find substantial differences exist in the out-of-pocket price of commonly used medications between under-insured and insured beneficiaries. These differences should attenuate with the expansion of Medicare to include a drug benefit decreasing the economic burden of multiple sclerosis.