Background: The effects of socio-economic status on mortality in patients with multiple sclerosis is not well known. The objective was to examine mortality due to multiple sclerosis according to socio-economic status., Methods: A retrospective observational cohort design was used with recruitment from 18 French multiple sclerosis expert centers participating in the Observatoire Français de la Sclérose en Plaques. All patients lived in metropolitan France and had a definite or probable diagnosis of multiple sclerosis according to either Poser or McDonald criteria with an onset of disease between 1960 and 2015. Initial phenotype was either relapsing-onset or primary progressive onset. Vital status was updated on January 1st 2016. Socio-economic status was measured by an ecological index, the European Deprivation Index and was attributed to each patient according to their home address. Excess death rates were studied according to socio-economic status using additive excess hazard models with multidimensional penalised splines. The initial hypothesis was a potential socio-economic gradient in excess mortality., Findings: A total of 34,169 multiple sclerosis patients were included (88% relapsing onset (n = 30,083), 12% progressive onset (n = 4086)), female/male sex ratio 2.7 for relapsing-onset and 1.3 for progressive-onset). Mean age at disease onset was 31.6 (SD = 9.8) for relapsing-onset and 42.7 (SD = 10.8) for progressive-onset. At the end of follow-up, 1849 patients had died (4.4% for relapsing-onset (n = 1311) and 13.2% for progressive-onset (n = 538)). A socio-economic gradient was found for relapsing-onset patients; more deprived patients had a greater excess death rate. At thirty years of disease duration and a year of onset of symptoms of 1980, survival probability difference (or deprivation gap) between less deprived relapsing-onset patients (EDI = -6) and more deprived relapsing-onset patients (EDI = 12) was 16.6% (95% confidence interval (CI) [10.3%-22.9%]) for men and 12.3% (95%CI [7.6%-17.0%]) for women. No clear socio-economic mortality gradient was found in progressive-onset patients., Interpretation: Socio-economic status was associated with mortality due to multiple sclerosis in relapsing-onset patients. Improvements in overall care of more socio-economically deprived patients with multiple sclerosis could help reduce these socio-economic inequalities in multiple sclerosis-related mortality., Funding: This study was funded by the ARSEP foundation "Fondation pour l'aide à la recherche sur la Sclérose en Plaques" (Grant Reference Number 1122). Data collection has been supported by a grant provided by the French State and handled by the "Agence Nationale de la Recherche," within the framework of the "Investments for the Future" programme, under the reference ANR-10-COHO-002, Observatoire Français de la Sclérose en Plaques (OFSEP)., Competing Interests: Sarah Wilson, Fabien Rollot, Mathieu Fauvernier, Laurent Remontet, Laure Tron, Marc Debouverie, Jérôme de Sèze, Thibault Moreau, Christine Lebrun Frenay, Pierre Labauge, Jean Pelletier and Olivier Dejardin report no disclosures. Floriane Calocer: received funding for the present research from the ARSEP foundation for a Postdoctoral Fellowship (payment to the institution), from the “Réseau Bas-Normand pour la SEP” for a Postdoctoral Fellowship (payment to the institution), from the Regional Council of Normandy (payment to the institution), from the Ecole Doctorale of Caen University for a training in LSHTD to conduct this research (payment to the institution). She received support for attending meetings and/or travel from the ARSEP Foundation (paid directly to herself, unrelated to this work). Sandra Vukusic: received grants or contracts (paid to her university hospital) from Biogen, BMS-Celgene, Janssen, Merck, Novartis, Roche, Sanofi-Genzyme and Teva; received consulting fees from Biogen, BMS-Celgene, Janssen, Merck, Novartis, Roche, Sanofi-Genzyme and Teva (paid to her university hospital); received payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from Biogen, Merck, Novartis, Roche, Sanofi-Genzyme and Teva (paid to her university hospital); received support for attending meetings and/or travel from Biogen, Merck, Novartis, Roche, Sanofi-Genzyme and Teva, participated on a Data Safety Monitoring Board or Advisory Board for Biogen (contracts with her university hospital), all of the above unrelated to this work. Emmanuelle Le Page: received payment or honoraria for consulting or lectures from Biogen, Merck, Teva, Sanofi-Genzyme, Novartis Alexion; received research support from Teva and Biogen, and received academic research grants from PHRC and LFSEP, and a travel grant from the ARSEP Foundation; received payment for consulting from Biogen, Merck, Sanofi-Genzyme, and Novartis; received invitations for national and international congresses from Biogen, Merck, Sanofi-Genzyme, Novartis Alexion, all of the above unrelated to this work. Jonathan Ciron: participated on a Data Safety Monitory Board of Advisory Board with Biogen, Novartis, Merck, Sanofi, Roche, Alexion and BMS-Celgene (all unrelated to this work). Aurélie Ruet: Consultancy fees from Roche and Biogen, payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from Merck, Roche, Biogen, research grants (paid to the institution) from Roche, Biogen and Sanofi-Genzyme, and support for attending meetings and/or travel from Biogen, Novartis and Alexion, all of the above unrelated to this work. Hélène Zephir: received research support for one PhD student from Roche, and research support for one MD student from FHU Imminent, consulting fees from Biogen IDEC (Symposium Biogen Idec in ISNI congress); received payment or honoraria for lectures from Merck, received payment or honoraria for lectures and boards from Novartis, all of the above unrelated to this work. David-Axel Laplaud: received payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from Biogen, Merck, Alexion, BMS, Roche and Novartis, all of the above unrelated to this work. Pierre Clavelou: received consulting fees from Biogen, Janssen, Medday, Merck, Novartis, Roche, Sanofi-Genzyme and Teva Pharma; and support for attending meetings and/or travel from Sanofi-Genzyme, and participated on a Data Safety Monitoring Board or Advisory Board for Medday, Merck and Novartis. All of the above unrelated to this work. Eric Berger: received consulting fees from Novartis, Sanofi Aventis, Biogen, Genzyme, Roche and Teva Pharma; received payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from Novartis, Sanofi Aventis, Biogen, Genyme, Roche and Teva Pharma (all of the above unrelated to this work). Olivier Heinzlef: consulting fees from Bayer Schering, Merck, Teva, Genzyme, Novartis, Almirall and BiogenIdec, support for attending meetings and/or travel grants from Novartis, Teva, Genzyme, Merck Serono and Biogen Idec and other financial or non-financial interests from Novartis, Teva, Genzyme, Merck Serono and BiogenIdec (all of the above unrelated to this work). Eric Thouvenot: received grants or contracts from Novartis and Biogen (paid to the institution), consulting fees from Merck, Novartis, Biogen and Celgene (paid directly to himself); received payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from Merck, Novartis, Biogen, Celgene (paid directly to himself). All of the above unrelated to this work. Jean Philippe Camdessanché: received grants or contracts from CSL-Behring, Grifols, Laboratoire Français des Biotechnologies, consulting fees from Akcea, Alexion, Alnylam, Argenx, Bristol Myers Squibb, Laboratoire Français des Biotechnologies, Pfizer, UCB Pharma, SNF-Floeger, received payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from Akcea, Alexion, Alnylam, Argenx, Biogen, CSL-Behring, Genzyme, Grifols, Laboratoire Français des Biotechnologies, Merck-Serono, Natus, Novartis, Pfizer, UCB Pharma and Teva. Received support for attending meetings and/or travel from Akcea, Alexion, Alnylam, Argenx, Biogen, CSL-Behring, Genzyme, Grifols, Laboratoire Français des Biotechnologies, Merck-Serono, Natus, Novartis, Pfizer, Teva, SNF-Floeger, all of the above unrelated to this work. Emmanuelle Leray: received consulting fees from Alexion, Merck, Novartis, Roche and Biogen, received payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from Sanofi Genzyme, and received support for attending meetings and/or travel from Sanofi Genzyme, all of the above unrelated to this work. Gilles Defer Received research grants (paid to institution) from Biogen, Merck Serono, Novartis, Sanofi Genzyme; payment for speaker honoraria from Biogen, Merck Serono, Novartis, Sanofi Genzyme, Teva Pharmaceuticals, BMS; funding for travel from Biogen, Merck Serono, Novartis, Sanofi Genzyme, Teva Pharmaceuticals; and personal compensation for scientific advisory boards from Biogen, Merck Serono, Novartis, Sanofi Genzyme, Teva Pharmaceuticals, and BMS. All of the above unrelated to this work., (© 2022 The Author(s).)