[The prevalence of multiple sclerosis in the city of Ourense, Galicia, in the north-west of the Iberian Peninsula].

Introduction: Multiple sclerosis is an inflammatory neurodegenerative disease of the central nervous system, which mainly affects young people of working and reproductive age, and represents the first cause of non-traumatic disability in this age group of the population. A north-south latitude gradient is recognised, with prevalence rates increasing as we move away from the equator. This gradient probably represents the genetic predisposition transmitted from the Scandinavian regions through the Viking invasions and could presuppose an influence of the vitamin D deficit related to a lower number of hours of sunshine per year.