Multiple sclerosis (MS) is a multifocal central nervous system disorder characterised by inflammatory demyelinating lesions affecting white and grey matter. MS affects quality of life of the patients and requires costy and long term treatments. OBJECTIVES: To determine the direct medical costs incurred in the treatment of relapsing remitting MS patients in the Social Security Mexican Institute (IMSS). METHODS: The data for this analysis were abstracted from the IMSS records, to be included each patient had to have at least 1 medical claim with a diagnosis of MS between January 1, 2008 and December 31, 2008. The patients records were used to obtain resource utilization over the year (including prescription drugs, clinician visits, surgical procedures, diagnostic procedures, etc), the costs were obtained from the IMSS public lists and were actualized to 2011 costs. RESULTS: A total of 172 patients were identified with a MS code, 52.33% (n=90) of them met the criteria for relapsing remitting MS. There were 54 female patients, with a female:male ratio of 1.5:1, with a mean evolution time of 7.21 years. The total average annual cost for each patient was MxP $173.970,64, 81.31% of which was attributable to the cost of prescription drugs, (80.5% was associated to the cost of disease-modifying drugs in particular (including interferon beta 1b, interferon beta 1a and glatiramer acetate); 16.2% to outpatient care (diagnostic and treatment-related procedures, office visit charges for usual care), 1.3% to inpatient care (diagnostic or treatment-related procedures, room and board charges, clinician inpatient visit and surgical procedures) and 1.16% to emergency room care (associated to disease exacerbation mainly). CONCLUSIONS: This analysis shows that prescription drug accounted for 81.31% of total relapsing-remitting MS related medical direct costs in the Mexican setting and that this costs are mainly associated with the use of disease-modifying drugs.