The concurrence of myeloproliferative neoplasms (MPNs) and multiple sclerosis (MS) is unusual. We report five patients from a localized geographic area in Denmark with both MS and MPN; all the patients were diagnosed with MPNs in the years 2007-2012. We describe the patients' history and treatment. A potential link between MS and MPNs has not been previously recognized. This observation calls attention to potential environmental factors and/or previously unrecognized genetic factors predisposing these patients to both MS and MPNs.