Background: Several studies have suggested that comorbid neurologic disorders are more common than expected in multiple sclerosis (MS).Objective: To estimate the incidence and prevalence of comorbid seizure disorders and sleep disorders in persons with MS and to evaluate the quality of studies included.Methods: The PUBMED, EMBASE, Web of Knowledge, and SCOPUS databases, conference proceedings, and reference lists of retrieved articles were searched. Two reviewers independently screened abstracts to identify relevant articles, followed by full-text review of selected articles. We assessed included studies qualitatively and quantitatively (I 2 statistic), and conducted meta-analyses among population-based studies.Results: We reviewed 32 studies regarding seizure disorders. Among population-based studies the incidence of seizure disorders was 2.28% (95% CI: 1.11–3.44%), while the prevalence was 3.09% (95% CI: 2.01–4.16%). For sleep disorders we evaluated 18 studies; none were population-based. The prevalence ranged from 0–1.6% for narcolepsy, 14.4–57.5% for restless legs syndrome, 2.22–3.2% for REM behavior disorder, and 7.14–58.1% for obstructive sleep apnea.Conclusion: This review suggests that seizure disorders and sleep disorders are common in MS, but highlights gaps in the epidemiological knowledge of these conditions in MS worldwide. Other than central-western Europe and North America, most regions are understudied.