OBJECTIVES Relapsing remitting multiple sclerosis (RRMS) is a chronic inflammatory disease that represents the most common chronic neurological disorder in young adults. RRMS often leads to disability and is a major cause of reduced working capacity due to neurological diseases. Aim of this study is to investigate patients’ working productivity during treatment with natalizumab. METHODS RRMS-Patients treated with natalizumab for a maximum of three months prior to baseline were eligible for study participation. Patients completed the EQ-5D and a questionnaire focused on occupational status, working ability, and days absent from work at study start study, after 6 months and 12 months. Socio-demographic and clinical data were collected. Primary endpoint was work productivity, which is defined as hours worked. To estimate costs and cost offsets due to the therapy with natalizumab, an average monetary value per working hour has been calculated to value productivity monetarily. RESULTS Preliminary results including 95 patients after 6 months of therapy show a significant increase in work productivity of 84 hours (p=0.014) for the whole study population compared to baseline. The average reduction of days absent from work was 4.8 days compared to baseline. The increase in working hours leads to an average change of monetarily valued productivity per patient and half-year from 6,550.40€ at baseline to 7,600.35€ after 6 months for the entire study population. A subgroup analysis has been run on the group of employed patients. The working hours increased significantly by 63h per half-year(p=0.025). CONCLUSIONS In this study, the preliminary results show a significant increase in work productivity, which leads to a significant increase in the monetary value of productivity, for RRMS-patients treated with natalizumab. An increase in working hours as well as a decrease in days absent from work led to an increase in monetarily valued productivity. Study was funded by Biogen-Idec.