The Swedish Multiple Sclerosis Register is a national register monitoring treatment and clinical course for all Swedish multiple sclerosis (MS) patients, with high coverage and close integration with the clinic. Despite its great value for epidemiologic research, it has not previously been validated. In this brief report, we summarize a large validation of amp;gt;3,000 patients in the register using clinical chart review in the context of the COMBAT-MS study. While further improving the data quality for a central cohort of patients available for future epidemiologic research, this study also allowed us to estimate the accuracy and completeness of the register data.