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Background: Multiple sclerosis (MS) is a chronic disease of the central nervous system, often resulting in significant neurological disability. The causes of MS are not known; however, the incidence of MS is increasing, thereby suggesting that changes in lifestyle and/or environmental factors may be responsible. On this background, the Environmental Risk Factors in MS Study or EnvIMS study was designed to further explore the etiology of MS. The design and methodology are described, providing details to enable investigators to (i) use our experiences to design their own studies; (ii) take advantage of, and build on the methodological work completed for, the EnvIMS study; (iii) become aware of this data source that is available for use by the research community. Methods: EnvIMS is a multinational case-control study, enrolling 2,800 cases with MS and 5,012 population-based controls in Canada, Italy, Norway, Serbia and Sweden. The study was designed to investigate the most commonly implicated risk factors for MS etiology using a self-report questionnaire. Results/Conclusions: The use of a common methodology to study MS etiology across several countries enhances the comparability of results in different geographic regions and research settings, reduces the resources required for study design and enhances the opportunity for data harmonization. © 2015 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]