Background: Good communication between patients and their health care provider (HCP) is essential for shared decision making (SDM). We developed a decision support tool (MS-SUPPORT) to improve SDM for multiple sclerosis (MS). MS-SUPPORT is an interactive, web-based tool to help patients clarify their treatment goals and preferences, learn about MS and disease-modifying therapies (DMTs), and prepare for their clinic visit. It generates a summary that can be shared with their HCP. Objectives: To assess the impact of MS-SUPPORT on patient-provider communication. Methods: We conducted a randomized controlled study comparing MS-SUPPORT to usual care. Adults with relapsing MS (PwMS) were referred through their HCP or patient support networks. Self-reported outcomes were assessed at baseline (T0), after viewing the MS-SUPPORT tool (T1), and after their clinic visit (T2). Communication was assessed separately by patients (using the COMRADE scale) and HCPs at T2. Decision quality assessed concordance between patient values and treatment plan. Results: 512 PwMS (85% female, 83% white) and 31 HCPs participated. 268 PwMS were randomized to MS-SUPPORT; 202 (75%) completed the tool and 87 (32%) shared the summary with their HCP. Most (85%) tool-completers reported at T1 that it would help them talk to their HCP. More HCPs in the tool versus control group reported as excellent: communication with their patient (84% vs. 80%), engaging their patient in decision-making (86% vs. 82%) and tailoring discussion about DMTs to what is important to their patients (85% vs. 81%), though these differences were not statistically significant. There was no impact on duration or the efficiency of the visit. Both patient groups reported excellent communication scores, with no difference between control and study groups (mean [standard deviation] 89.3 [11.5] vs. 88.1 [13.21], p=0.38). Those who completed more of the tool had higher scores (84.3 [19.1] in non-completers, 90.2 [10.8] in completers and sharers). Decision quality was high in both groups at baseline and increased by 9% between T0 and T2, with no difference between groups. Conclusions: MS-SUPPORT appears to improve patient-provider communication from the perspective of HCPs but not patients, though higher scores were noted among those who completed more of the tool. High scores in the control group, with improvement over time, suggest that selection and response biases may have affected our findings. Funding was provided by EMD Serono Inc., USA, an affiliate of Merck KGaA, Darmstadt, Germany, through MS-LINK, a consortium to improve patient outcomes by advancing MS science to generate real-world data and patient-centered solutions. Further MS-LINK research is designed to close existing scientific gaps to improve outcomes. Editorial support was funded by the sponsor and provided by Ashfield Healthcare Communications (New York, NY, USA). Authors had full control of the abstract and provided final content approval.