Multiple sclerosis (MS) is the most common chronic disabling disease of the central nervous system in young adults. Early onset and long duration of disease result in tremendous individual, family, and societal costs as well as reductions in quality of life and work productivity. Persons who have MS have a higher prevalence of a number of psychiatric symptoms and disorders. This article seeks to summarize the existing literature on the epidemiology, impact, and treatment of psychiatric disorders among persons who have MS and to identify the areas in which further research is needed.