Background: An estimated 85% of persons with multiple sclerosis (MS) present with relapsing-remitting (RRMS) disease. There are few large multi-state observational data sources in the United States (US) that are able to prospectively track MS disease activity and progression. The Corrona MS Registry was launched in 2017 in collaboration with the National MS Society to study longitudinal disease history, and safety/effectiveness of MS disease modifying therapies (DMTs). Objectives: To characterize RRMS patients enrolled in the Corrona MS registry. Methods: The Corrona MS Registry is a US national multicenter, observational patient registry collecting clinician- and patient-reported data from neurologists treating adult MS patients during routine care visits. A descriptive analysis was performed of demographics and clinical and patient-reported disease activity measures, to characterize RRMS at the time of enrollment into the MS Registry. Results: As of December 31, 2020, 1,331 of 1,573 (84.6%) MS patients were diagnosed with RRMS at the time of enrollment. 76.9% of RRMS were female, with mean age and disease duration of 49.2 and 12.1 years, respectively. Mean number of relapses in the 12 months prior to enrollment was 0.3. 36.0% reported cerebral (or mental function) system involvement on initial disease presentation. Among 1,163 (87.4%) RRMS on DMTs with a Clinical Global Impression of Change (CGI) assessment, 513 (44.1%) had some level of improvement while on their current DMT. Median timed-25-foot walk was 5.8 seconds (n=1,097); 61.0% (808/1,324) had no or mild disability as measured by the Patient Determined Disease Step (PDDS) score; mean correct score on the Symbol Digit Modalities Test (SDMT; n=1,148) was 49.2; and mean Multiple Sclerosis Impact Scale (MSIS-29) on the psychological subscale (n=1,307) was 29.2 vs 24.8 on the physical subscale (n=1,287). Mean overall work impairment due to MS as measured by the Work Productivity & Activity Impairment Questionnaire (WPAI) was 19.4% (n=680 of 759 RRMS currently employed), and mean non-work activity impairment was 29.3% (n=1,297). Conclusions: Preliminary data from the Corrona MS Registry at enrollment suggest that the cognitive ability and mental function of RRMS patients may be impacted disproportionately compared to physical function. Early detection of cognitive impairment and intervention in this stage of disease may help patients improve mental function and experience less work impairment.