OBJECTIVES: PatientsLikeMe is an online health-data sharing community and research platform for patients with chronic and life-changing health conditions. In developing the PatientsLikeMe online platform for patients with Multiple Sclerosis (MS), we required a patient-reported, multi-dimensional assessment of functional status that was easy to complete. Existing measures of functional status were inadequate; clinician-reported, focused on walking, and burdensome to complete. To develop a longitudinal record accessible to patients using the site, we developed the Multiple Sclerosis Rating Scale (MSRS). METHODS: We adapted a clinician-rated measure, the Guy’s Neurological Disability Scale, to a self-report scale and deployed it to an online community. As part of our validation process, we reviewed online forum discussions between patients, conducted in-person patient cognitive debriefing, and made minor improvements to form a revised scale (MSRS-R). The MSRS-R was deployed as a cross-sectional survey to 4382 patients with relapsing-remitting MS (RRMS) on the PatientsLikeMe platform.  The survey included the MSRS-R as well as a range of comparator MS measures: PRIMUS, MSIS-29, PDDS, NARCOMS Performance Scales, and MSWS-12. RESULTS: In total, 816 RRMS patients responded. The MSRS-R exhibited high internal consistency (Cronbach’s alpha = 0.86) and 1-week retest reliability (r = 0.91). The MSRS-R walking item was highly correlated with alternative walking measures (PDDS, r = 0.84; MSWS-12, r= 0.83; NARCOMS mobility question, r = 0.86). The MSRS-R correlated well with comparison instruments, and reliably differentiated between participants by PDDS disease stage, relapse severity, and time since diagnosis.  Retrospective scoring of most recent relapse suggested a 3-point increase in MSRS-R might usefully identify relapses. CONCLUSIONS: The MSRS-R is a concise, multi-faceted measure of MS-related functional disability.  It may be useful for describing the impact of MS and can support further inquiry into the factors that relate to variation in outcomes among MS patients.