Multiple sclerosis (MS) is a multifactorial disease where both environmental and genetic risk factors play a role. More than 50 genetic polymorphisms have been identified in association with MS mostly by mapping close to genes involved in immunoregulation. Several environmental factors have been associated with risk for developing MS, including smoking, obesity, EBV infections, and lack of sun exposure. Interactions between major genetic risk factors and environmental exposures have been observed making it possible to begin to form groups of risk factors that are jointly involved in MS pathogenesis.