Purpose: The goal of this study was to evaluate clinical outcomes and patient-reported outcomes (PROs) over 12 months in patients with relapsing multiple sclerosis (RMS) who switched from glatiramer acetate (GA) to delayed-release dimethyl fumarate (DMF) 240 mg BID after suboptimal response to GA in real-world clinical practice., Methods: The RESPOND (Effectiveness of DMF and Its Impact on PROs in Suboptimal GA Responders With RMS) study was a Phase IV, prospective, multicenter, open-label, single-arm, 12-month observational trial. The study was conducted in the United States at 63 sites between August 2013 and February 2016. Patients diagnosed with RMS who experienced a suboptimal response to GA (defined as perceived suboptimal efficacy, intolerance, or poor adherence to GA) were eligible for enrollment. DMF treatment was initiated within 60 days of enrollment. The primary objective was to estimate the annualized relapse rate (ARR) at 12 months based on data collected from medical records and compare it with the 12 months before DMF initiation. Secondary objectives of the study included assessing the change in PRO scores from baseline to 12 months; PROs were recorded before and at 6 and 12 months after DMF initiation., Findings: Of the 318 patients included in the analysis population, 247 (78%) completed treatment. Mean (SD) time on GA treatment before switching to DMF was 51.3 months (49.1 months). The ARR (95% CI) reported for the 12 months before DMF initiation was 0.49 (0.42-0.57) compared with 0.11 (0.07-0.17) at 12 months after DMF initiation, representing a 78% reduction in ARR (P < 0.0001). Statistically significant improvements from baseline were observed for multiple PROs, including the 36-item Short Form Health Survey physical and mental component summaries (P = 0.0201 and P = 0.0014, respectively), the 5-item Modified Fatigue Impact Scale (P = 0.0002), the 14-item Treatment Satisfaction Questionnaire for Medication (P < 0.0001), and the 7-item Beck Depression Inventory (P = 0.0117)., Implications: DMF may be an effective treatment option in patients with RMS who experience a suboptimal response to GA. The results should be interpreted with caution due to the observational nature of the study and the lack of a control group. Other limitations of the study include a potential bias due to regression to the mean and lack of randomization. ClinicalTrials.gov identifier: NCT01903291., (Copyright © 2018. Published by Elsevier Inc.)